embryo, it would be close below, and only a little behind, the fore end of the creature; in this supposed type the notochord would be only a little behind the punctum terminale.

Now the fore and mid brain have at present only yielded to embryologists one pair each of segmental nerves growing from their dorsal region; the hind brain is a series of enlargements.

The two great pre-aural segmental nerves (5th and 7th) by the overfolding of the brain, are enabled to send on to the front of the head their special branches, needed there, because of the specialization (for motion) of the third, and the specialization (for sensation) of the first nerve.

Thus these three-branched nerves have grown in harmony with the paired and unpaired basi-neural cartilages, and there is a due extension forward of cartilages to the partially straightened skull, and a due supply of nerves from behind.

But in spite of all the metamorphoses of these parts, neural and skeletal, if Dr. Milnes Marshall's observations (with which mine accurately accord) be true, then we still have two true segments in point of the cleft (oral) which is forked over by the 5th nerve. It could not be expected that the visceral arches and intervening clefts would be otherwise than greatly modified and masked in the fore part of the head, with its huge nervous centres, and highly complex organs of special sense.

The larvae of the Amphibia, especially of the " Anura,” have been very carefully studied by me, as likely to throw light upon the order of development of the cranial-facial skeleton; the lamprey, also representing those larvæ permanently, has been the subject of much thought, as a sort of practical pattern of those larvæ. In these forms the extra-visceral skeleton of the head is much developed, and only part of the true visceral (internal arches) appear.

For the mouth in these forms is terminal, and its skeleton is made up of sub-cutaneous cartilages, the serial homologues of the subcutaneous basket-work of the large respiratory pharynx of the lamprey.

In that form the only true visceral arches developed are the mandibular and the hyoid; a basal rudiment of the internal branchial arches exists as the "lingual cartilage."

The free mandible of the lamprey is packed up, and apparently functionless, close behind the postero-superior "labial;" the quadrate portion of the "suspensorium," is a mere point or style, with no condyle.

This suspensorium throws a fold of cartilage over the second branch of the 5th nerve and the temporal muscle; this is not the pterygoid cartilage, and is only seen in this type, in tadpoles, and in some chondrosteous Ganoids, e.g., Planirostra, as shown by Mr. Bridge.

Also the epi-hyal is in a low state of development; there is a cerato-hyal and a basi-hyal piece, growing forward below, in front of the large lingual ("basi-branchial") cartilage.

But there is a copious growth of external cartilage both around the terminal mouth and around the huge branchial pharynx; the cranial box is at a low state of development, and the fore part of the head shows no trace of a pre-oral arch.

In tadpoles we have a very similar state of things, but there is a real ascent; the suspensorium develops a quadrate condyle, and on this the passive mandible is hinged.

Round the mouth, cartilages quite like those of the lamprey, are developed, but they are smaller; and there are only four bars (pouches) in the walls of the pharynx; rudiments of four true intrabranchials also, are developed. A fifth subcutaneous cartilage appears during metamorphosis, belonging to the mandibular arch; it becomes. the cartilaginous "annulus tympanicus."

After it has appeared the "styloid cartilage" of the lamprey ("epi-hyal") is, in them, slowly developed, and becomes the "columella auris."

Also, during metamorphosis, the rudiment of a "palatine" visceral arch appears, and in the genus Bufo becomes a large distinct pre-oral cartilage. After metamorphosis, another cartilage appears on each side, within the nasal cleft, the "pro-rhinal."

My idea of the order, in time, of the skeletal elements is as follows:

First. The superficial cartilages of the mouth and respiratory pharynx.

Secondly. Basi-neural, and then, afterwards, going from them, visceral cartilages, in the inner layer of the walls of the mouth and throat.

Thirdly. After that, selection of dermal scutes, first as scales and afterwards as splint-bones ("parostoses "), to supplement, for supporting purposes, the chondro-cranium.

Fourthly. A gradual arrest, and then more or less of suppression, of the chondro-cranial parts, and the increased use of subcutaneous investing bones, at times in conjunction with remnants of the old primary superficial cartilages.

The development of the spine has been, I believe, a thing of later date; and the limb-girdles and limbs newest and latest of all.

The brain, mouth, and throat, with coiled intestines, whose outlet is very little behind the occiput, make up all that is of any consequence, in such a form as the gigantic tadpole of the paradoxical frog (Pseudis); whose post-cranial segments have evidently been super-additions, developed for the sake of locomotion-to form a mere swimming organ.

Behind the head, the segments for free motion cannot be moved by the developing segmental muscles until an intercalary segmentation has taken place; hence the vertebral segments which come between the "muscle-plates" and spinal nerves.

The head, eschewing such mobility, has developed an axial box for the brain, and beneath this firm structure, the mobile and distensible mouth and throat are swung.

III. "On an Extension of the Phenomena discovered by Dr. Kerr and described by him under the title of A New Relation between Electricity and Light.'" By J. E. H. GORDON, B.A., Assistant Sec. of the British Association. Communicated by Professor TYNDALL, F.R.S. Received February 10, 1879.

In November, 1875, Dr. Kerr announced in the "Philosophical Magazine," that he had discovered a new relation between electricity and light. He showed that when glass is subjected to an intense electrostatic stress, that a strain is produced which causes the glass to act like a crystal upon polarized light.

On Wednesday, February 5, 1879, I was working at this experiment in the Royal Institution, and endeavouring, by means of the electric light, to project the effect on a screen, in preparation for a lecture on the next day.

In the experiment as described by Dr. Kerr, and which was shown plainly on the screen, on February 6, the light is extinguished by the Nicols, and reappears when the coil is set going.

In the projection experiment a patch of moderately bright white light, about 3 inches diameter, appeared on the screen when the coil was worked. The images of the points inside the glass were about 1 inches apart. On Wednesday, however, the electrostatic stress was accidentally allowed to become strong enough to perforate the glass. Immediately before perforation there occurred the effects which are the subject of the present communication.

First appeared a patch of orange-brown light about 6 or 7 inches diameter. This at once resolved itself into a series of four or five irregular concentric rings dark and orange-brown, the outer one being perhaps 14 inches diameter. In about two seconds more these vanished and were succeeded by a huge black cross about 3 feet across, seen on a faintly luminous ground. The arms of the cross were along the planes of polarization, and therefore (the experiment being arranged according to Dr. Kerr's directions) were at 45° to the line of stress.

The glass then gave way, and all the phenomena disappeared except the extreme ends of the cross, and the discharge through the hole, where the glass had been perforated, was alone seen.

The phenomena were seen by Mr. Cottrell, by Mr. Valter (the second assistant), and by myself. A fresh glass plate was at once drilled in hopes of repeating the phenomena in the lecture next day, but owing to sparks springing round we did not succeed in perforating the glass, and therefore saw only the faint return of light described by Dr. Kerr.

Some more glasses have been prepared and their terminals insulated, and I now propose to make another attempt to repeat the new effects before the Royal Society.

February 20, 1879.

THE PRESIDENT in the Chair.

The Presents received were laid on the table, and thanks ordered for them.

The following Papers were read :—

I. "On Electrical Insulation in High Vacua." By WILLIAM CROOKES, F.R.S. Received February 6, 1879.

The experiments here described were tried nearly two years ago. They were suggested by some observations I was then making on the passage of an induction current through highly exhausted tubes. The main branch of the research being likely to occupy my attention for some time, I may be unable to return to these less important offshoots. I have ventured, therefore, to embody them in a short note for the "Proceedings of the Royal Society."

A pair of gold leaves were mounted, as for an electroscope, in a bulb blown from English lead glass tubing. The leaves were attached to a glass stem and the lower part of the bulb was drawn out for sealing to a Sprengel pump as shown at fig. 1. A stick of ebonite excited by friction was generally used as the source of electricity, but any other source will do equally well, provided it is not too powerful.

No special attention was paid to the action of electricity on the leaves in air or at moderate vacua, as it agreed with what is already well known. The exhaustion was pushed to a very high degree (about the millionth of an atmosphere), when it was found that the excited

ebonite had a much greater effect on the gold leaves than at a lower exhaustion; for a long time however I was not able to charge the leaves permanently, in consequence of their falling together as soon as the source of electricity was removed.

FIG. 1.

When a hot substance was brought near the bulb facing a gold leaf, so as to warm the glass, molecular repulsion took place, and the leaves retreated from the warm spot, standing out at an angle of about 45°. As the glass cooled the leaves resumed their former vertical position.

While the leaves were repelled from the hot glass, the excited ebonite had a very powerful action on them, and if it were brought near hastily, the leaves flew off to the side of the glass, destroying the apparatus. By careful management and repeated trials, however, the ebonite could be brought near the warm spot of glass, the leaves suddenly extending at an angle to each other. The appearance was as if a spark had been able to pass across the bridge formed by the line of advancing and retreating molecules connecting the hot glass with the gold leaves. On the ebonite being removed and the glass allowed to cool, it was found that the repulsion of the leaves was permanent. The rubbed ebonite would attract and repel them as it was moved to and fro, but the angle formed by the leaves with one another remained unchanged. A warm body brought near the glass opposite one leaf would repel the pair as a whole; on then warming the opposite side of the glass repulsion on that side took place, the angle of the leaves being somewhat diminished, but on cooling the leaves opened again to their former extent.

When the glass bulb was strongly heated by a spirit flame the leaves suddenly discharged and fell together.

Another bulb (fig. 2) was prepared, containing a plate of mica, a, which could be suddenly placed between the gold leaves, bb. The