There remains among the Physophoridæ, closely resembling in general outline the type Agalma, several genera which should be mentioned in this place. One of these is so well marked that it can be easily distinguished at a glance, and in one important particular is different from all the other Physophores. It will be remembered in my account of the arrangement of the swimmingbells of Agalma, published in the first article of this series, that I described these organs as arranged in two rows, the lines of the two series apparently opposite on the axis. As is true also of other genera, where nectocalyces occur, this appearance of being placed in two rows on different sides of the stem, is brought about by a twisting of the axis itself, and not by a formation of the bells on opposite sides. If the axis of Agalma has its fibers straightened, all the covering-scales, swimming-bells and the like, would be found one above the other in a line. Consequently the biserial arrangement of the swimming-bells is wholly distinct from their place of apparent origin on the axis, but dependent upon the twisting of the axis itself. In the genus Stephanomia,1 instead of the section of the stem between the position of origin of two nectocalyces taking a turn through an angle of 180°, thus bringing the nectocalyces into two series; the stem between two adjoining swimming-bells is twisted at a smaller angle, even one less than a right angle, so that the openings of the bell cavity face on all sides. There still remains a serial arrangement of the bells, but in Stephanomia it is no longer biserial as in Agalma, but multiserial with the bells opening in all directions in a plane at right angles to the axis. The polyp-stem in this beautiful genus resembles that of an Agalma, but the feeding-polyps are mounted upon long peduncles, so that the tentacles seem to originate on the polypites midway between the stem and the mouth. Covering-scales of peculiar outline are also present, as well as "tasters," and male and female sexual-bells. In all of these structures, the genus is very characteristic, and if its whole organization be considered, is probably the highest member of the family. The arrangement of the swimming-bells, opening as they apparently do on all sides of the stem, make it possible for the whole colony to move rapidly through the water, and nothing can excel the grace with which these animals make their way through 1 This genus was commonly called Foskalia by European naturalists; Stephanomia has a prior claim as its true name. g.. their native element, when the combined movements of different series of bells impart a spiral motion to the whole colony. In truth, the grace of this animal is something marvelous, and when once seen is not soon to be forgotten. There are two genera of Physophores closely resembling Agalma in external shape, but so well marked that they are commonly placed in different genera. They are known as Agalmopsis, and Halistem The likeness of the former of these animals to Agalma, as its name betrays, is very great (Fig. 121). The most important difference between the two is in the structure of the tentacular-knobs, which in Agalmopsis (Fig. 13) have but a single terminal filament, while in Agalma, as has been already pointed out, there are two of these terminal fila FIG. 12. Agalmopsis. diate vesicle. In minor The genus called Hal- թ. S........ 13 FIG. 13.-Pendant tween Agalmopsis and knob of Agalmopsis. 1 Figs. 12 and 13 are copied from my paper in the Bull. Mus. Comp. Zool., Vol. VI, No. 7. Agalma, lies in the form and arrangement of the pendant tentacular w FIG. 14.-Apolemia. knobs. In Halistemma as in Agalmopsis, there is but a single terminal filament on each knob, but there is no involucrum such as we have already shown covers the "sacculus," or body of the knob in Agalma. Moreover, these knobs do not hang from tentacles, but each one is suspended separately from the base of the polypite, and what appear to be tentacles are in reality their pedicels very much elongated. All the genera mentioned in the previous pages constitute a natural group of float-bearing jelly-fishes. They are closely allied to one another, and all possess an air bladder or float. There remains one more genus to be described, which is doubly interesting from its great size and its relationship to a group of tubular jelly-fishes which has little in common with Agalma. This genus is called Apolemia, and is known to the Italian fishermen, on whose shores it is most abundant, as the "lana di mare," or wool of the sea. It often reaches, when extended, a length of from twenty to thirty feet, and is seldom found entire, but generally in the form of broken fragments like that figured in Fig. 14.1 The main difference between Apolemia and Agalma lies in the fact, that while in the latter the covering-scales are fastened along the whole length of the polyp-stem, and no visible break occurs where these structures are not found, in Apolemia the feedingpolyps and covering-scales are united together in clusters at intervals on the stem, separated from each other by a bare portion (d) of the axis, which is destitute of appendages of any kind. The fragment figured above gives a general view of a portion of such an Apolemia, but if the whole colony were figured and the remainder of the axis shown, upon one end would be found a float just as in Agalma, and four or five pairs of swimming-bells, arranged in a like biserial manner. There is, however, this peculiarity of the portion of the stem, which bears the nectocalyces in Apolemia, that from it also hang bodies closely resembling " tasters," yet destitute of tentacular filaments. This is, as far as I know, the only instance among the Physophorida where the nectostem has tasters arising from it. They are not as a consequence found along the polyp-stem as in most other genera. If now we turn our attention to an examination of the clusters of bodies arranged at intervals along the polyp-stem as in Fig. 13, we find each cluster of peculiar shape, differing greatly from 1 The figure (Fig. 14) was copied from the Bull. Mus. Comp. Zool., Vol. VI, No. 7. what we have already studied. The stem, half way between each cluster (r), is jointed so that as the animal grows, or the stem elongates, that cluster most distant from the float ruptures its connection with the colony at the joint in the axis, and when separated from the remainder, leads an independent life. It thus happens that these little clusters are often found floating alone in the water, hanging from the fragment of the stem, having broken their connection with the parent, or rather with the colony, to which they were formerly attached. As is also the case in a larval stage of a common jelly-fish, Aurelia, known as the strobila, which is, however, attached at one extremity to the ground, successive terminal members continually separate from the collection and swimming away, develop into new Aureliæ, so terminal clusters of the free-swimming Apolemia are successively broken off from the colony as it matures. The likeness between the method by which Aurelia and the clusters of Apolemia develop is morphologically very great. Let us consider the composition of a single cluster which has separated in this way from the colony, and see how far this likeness can be traced. The fragment of an Apolemia ruptured from the remainder of the colony, resembles closely in shape a number of transparent spheres fastened together by one pole, from which hang down a number of polyp-like organs. The cluster is, in the main, composed of many jelly-like bodies joined together on the fragment of the stem. These bodies are but modified covering-scales, and are generally penetrated by a single tube, just as is found universally to be the case among other genera. The covering-scales are carried uppermost as the cluster floats in the water. From the lower side, and also attached to a segment of the axis, there hangs down the same flask-shaped feeding-polyps (ƒ), which have been described in Agalma. The tentacles (c) of the feedingpolyps do not bear pendants as are found in all the other Physophores except Physalia. In each cluster of polyps there are two flask-like bodies, in general shape not different from the remaining, which have a bright red color. We are unable to assign any reason for this peculiar coloration in these two feedingpolyps. Lastly, in each cluster of the Apolemia colony we find sexual-bells, male and female, which fill out the complement of organs necessary for the independent life of the cluster. On account of this independence of life in each cluster, when |