one and the same species (Mougeotia calcarea, Clev.), the formation of the spores may take place equally in the manner of the three abovementioned genera; also that occasionally even the spores may be formed without any conjugation, and further that in a plant found growing last October in an aquatic stone house in the Upsala Botanical Gardens, and which is described as Gonatonema ventricosum, the spores are formed in a neutral way through the agency of cells never intended for and incapable of conjugation. Such spores the author calls agamospores, and he finds a second species of this new genus in Hassall's anomalous Mesocarpus notabilis.

If the interpretation placed on the phenomena to be witnessed in the Mesocarpeæ by Prof. Pringsheim be accepted, then this family can scarcely be left among the Conjugatæ, and this would hold true also of Wittrock's new genus, as indeed is so stated by himself. But may not the phenomena be interpreted in yet one other way? First, as to the agamospores in Gonatonema. Is it beyond the bounds of possibility that, despite their external likeness to zygospores, these are simply vegetative spores, to be compared to one of the so-called tetraspores in Floridea? They surely cannot be compared to any form of organism itself the product of the commingling of the contents of two different cells! Another suggestion, to account for this agamospore, has been made to me by my friend William Archer. It is that there may have been a separation between the upper and lower portions of the protoplasmic contents of the same cell, and that these, without waiting for the formality of forming separate cells, may have then and there conjugated. This is certainly a most ingenious suggestion, and is stengthened by the well-known fact that, in some Desmids, after the single-celled frond has divided into two halves, and before the newer portions grow into anything like the similitude of the older portions, the two halves, which were only just parted, will conjugate and form an ordinary zygospore. De Bary gives some pretty figures of this strange phenomenon, which, according to Mr. Archer, might be carried one step further, and there be no parting at all. In favor of my own idea I can only add that the first origin of what, in some of the Florideæ, will form the tetraspores, and the origin of these agamospores, appear to me to be the same. Next as to the sporocarps in

Mesocarpus. The differentiation into sexual entities of the protoplasmic contents of cells is confessedly, at first, scarcely perceptible. It would be impossible, in many cases, to say with any confidence, this one is the germ cell, and that one is the sperm cell. But gradually a differentiation appears in that the contents of the former exhibit themselves as passive, and of the latter as active; the contents of the one remain quiescent, those of the other pass over to conjugate with the former, but all through the contents that commingle are almost in every case alike in quantity. Carry the differentiation a step further on,

and

we find that the contents that commingle may be at first somewhat, and then be strikingly unlike in quantity. The passive contents will be divided into a comparatively small number of portions (in Fucus eight), but these each can be fertilised by the very smallest portion of the active contents. Now may not the Mesocarpeæ be a link between these groups? The contents of each of the two cells divides into certain portions. The fertilising power of the active contents is not sufficient for the passive contents, and hence but one portion-that the most specialized-is fertilised; this forms the zygospore; the other portions remain sterile. Then this spore would differ from the zygospore of Zygnema just in the same proportion as it would differ from the oospore of Fucus, but the fructification would not at all be a representative carpospore, and the at first sight very anomalous case of M. calcarea may be explained by supposing that the number of partitions is a matter of but secondary importance, unless the fertilising power of the active contents were to increase. This field of research is an important one, and much as we are indebted for information on these points to the labors of the Swedish botanists, we must still continue to look for fresh facts and new explanations.

E. PERCEVAL WRIGHT.

ON THE STRUCTURE OF BLOOD-CORPUSCLES. AT the "Physiological Laboratory," University of Michigan, Dr. C. H. Stowell has continued his study on the structure of the red blood-corpuscles.

The method employed is that given by Professor Boettcher in the Archiv für. Mic. Anat. Bd. 4.

The corpuscles are "bleached" by means of a saturated solution of corrosive sublimate in 96 per cent. alcohol. Into fifty parts of this solution one of blood is rapidly diffused.

In twenty-four hours the super-incumbent fluid is poured off and alcohol added. In twenty-four hours more this is poured off and distilled water added.

The corpuscles are then subjected to staining agents, carmine being preferred.

Three classes of corpuscles are seen.

Ist--Homogeneous and shiny.

2d-Those having a nucleus; and

3d-Those having a well-marked nucleus and nucleolus.

The July No. of New Preparations contains the following

account of recent experiments. Dr. Stowell says:

"My experiments were performed on cats and rats, poison

ing them with solutions of corrosive sublimate-in some cases bringing on death immediately, in others not until the lapse of several days. The blood was examined both before and after death, and no change was discerned in the appearance of the blood-corpuscles, except in a few instances, when there was noticed some change in their shape. This is not what one would anticipate from a perusal of Prof. Boettcher's article.

'However, by following the method given in the last number of your journal, we have demonstrated this nucleus in the red corpuscle of man (as previously reported), the dog, cat and rat. The most satisfactory result was obtained from the blood of the rat; the most unsatisfactory from that of man. however, is attached to this fact.

No value,

"By using higher powers than at first employed, we are positive there is a granular appearance to this nucleus, not present in other parts of the blood cell. In some cases this is quite marked, especially when the nucleus is large; and also in those corpuscles where we have seen a nucleolus, this granular structure is very evident. This is what we should expect when accepting Beal's theory of protoplasmic matter.

"In some specimens examined, the proportion of nucleated to non-nucleated cells was very small indeed, while in other specimens the proportion was much greater."

A STANDARD MICROMETER.*

BY R. HITCHCOCK.

The subject that I wish now to bring before this convention is of such importance that it seems hardly necessary to say anything to call your attention to it.

The need of a definite and accurate standard for microscopic measurement has been recognized by some for many years. As an example of this, Prof. Lyons, in 1857, proposed to the British Association for the Advancement of Science that "some definite micrometric integer should be assumed, being a determinate part of unity." He suggested as a name for this integer, that it should be called a micro-line, and thought that a good provisional standard would be the 1-10000 of an English inch, but his preference was for a decimal scale.

* Abstract of a paper read at the National Microscopical Congress, Indianapolis, Aug. 16, 1878.

No action seems to have been taken in the matter at that time or since.

We are as far from a definite standard to-day as we ever were, and unless the question is taken up in good earnest by able and well-known men, representing in some way the microscopists of the country, either as delegates from societies to a convention like this or at a special meeting for the purpose, it will be as it is now for years to come.

If we pretend to scientific accuracy in our work we must have reliable micrometers; and, if we desire to avoid trouble in reading the results of the labor of others we must all use the same unit of measurement.

If well chosen, our standard will be adopted by other countries, and we have a good opportunity now to make this congress remembered in the history of our science.

To secure our standard, Prof. Rogers promises to place in the hands of a properly appointed committee, representing five of the leading microscopical societies of the country, six standards consisting of fifty spaces, covering exactly part of the standard British yard at Washington. Each of these spaces would be divided into 10 equal parts, thus giving 500 lines. These lines would be 1-1000th of an inch apart. Prof. Rogers then goes on to say as follows:

"This committee shall ascertain that these six micrometers are comparable within certain very narrow limits. I will then present one to the properly appointed custodian of each society, and retain one for myself. I can then at any time make duplicates of a common standard."

I should add that Prof. Rogers is now having a new machine made, which he has reason to believe will enable him to do better work than the one he is now using. Even with the one he now has, he can arrive very near the truth.

Some of his earlier micrometers are not reliable, and all made previous to May, 1877, belong to this class. The errors of these range from zero up to 1-7000 of an inch.

By perfecting his machinery in various ways, this error has gradually been made less, until it became about 1-40000 of an inch in maximum; but a few weeks ago even this residual error was accounted for, so that now, Prof. Rogers believes he can rule one hundred micrometers just alike.

We can all realize that it has required a great deal of patient observation and experimenting to arrive at this result.

We are accustomed in this country to employ the divisions of the inch. As a rule people are conservative. But, in a case like this, custom must not govern us. We decide this question, not for ouselves alone, but for future generations. The action of this congress will be known throughout the world, and its influence must be felt. It becomes us, then, to act carefully and with the best judgment.

We propose a standard for universal use; then let us select one that can and will be adopted, not alone by our own country, but by all civilized nations. We must not allow considerations of economy to actuate us, nor of mere convenience. Therefore, I say, let us select the French metric system as our basis of measurement.

It is not for me to indicate to this audience its advantages as a system of measurement for universal use. I do not even say that I believe it is the best. But I do say, that it is the only system that can be made universal in a micrometer for the microscope, and in this I expect the support of all who are familiar with scientific work throughout the world. To those who are in doubt as to this, it is sufficient to remind them that a nation like the French, which has used a decimal system so long, could not be expected to change it for one with divisions like our inch. We should be ready to sacrifice something ourselves (and it will be, at most, a sacrifice to us for a short space of time) for the sake of securing uniformity with the people of a whole country. Moreover, even in our own country the inch standard cannot be maintained, for scientific men are decided in their preference for the French system. When I say that this congress has the power to make a standard for the country, I mean on condition that it be made to suit the requirements of men of science. Practically, we are forced to the adoption of the French system, by the demands of our own workers. I have not been able to collect statistics as to how many of our educational institutions are now using the millimeter micrometers, but I know that many of them are, and I know, too, that a chemist can hardly be found who measures in quarts, and pints, and gills, or who weighs in grains. It is always centimeters and grammes, and