2;J Prof. H. J. Clark on Lucernaria. 



cell-like bodies extend in close proximity from the outer to the 

 inner wall, so that, in a section of the thickness of the disk, it 

 appears to be transversely striated. In the peduncle, as a trans- 

 verse section reveals, these columnar cells are arranged about 

 the axis, in peculiar regular groups : some columns pass from 

 one channel to the next on either side, some diagonally across 

 the axis from one channel to an opposite one, and others extend 

 obliquely from the channel to the muscular cords which alter- 

 nate with them. This ai'rangement reminds one of the me- 

 thodical disposition of the great cells in the body of Pleurohra- 

 ckia*, as I have described them in Prof. Agassiz's third volume of 

 his ' Contributions to the Natural History of the United States.'' 

 In the oral or lower side of the disk of Aurelia, the gelatiniform 

 substance has the same structure as in the aboral side, while in 

 Lucernaria, although it has all the regularity in the disposition 

 of its components that obtains in the aboral side, yet it possesses 

 a totally different nature, as I will describe hereafter in connexion 

 with the muscular system. 



* At the time the investigation of the gelatiniform mass of Pleurobrachia 

 rhododactyla, Ag., was made, I had not in my possession lenses of the 

 proper definition and working-distance to make out the histological ele- 

 ments with the accm-acy that such excessively transparent bodies de- 

 mand, and therefore, using inferior lenses, I fell into an eiTor which I am 

 only too glad to correct. Since that time I have obtained one of Tolles's 

 half-inch objectives, with an exceedingly sharp definition and an extra- 

 ordinary working-distance; so that I have been enabled to work with per- 

 fect freedom upon the living animal, and without injuring its tissues in the 

 least. What formerly I mistook to be the outlines of the walls of enormous 

 cells are in reality elastic fibres. The mistaking the fibres for the profile 

 of cell-walls does not aff'ect the arrangement in the least as I formerly 

 described it, and which I have since verified with my new objectives. The 

 elastic fibres assume various forms, according to the degree of expansion 

 or contraction of the animal ; sometimes they are perfectly straight, and at 

 others they are contracted either in a loose spiral, or retracted into a close 

 eoil. This is most easily observed in young specimens. In the young of 

 another Ctenophoran, viz. Bolina alata, Ag., about Vir of an inch in dia- 

 meter, at which size its pro]iortions, shape, the considerable depth of the 

 tentacular sockets, and the length of its tentacles render it remarkably like 

 a Pleurobrachia, the elastic fibres are very few, but quite conspicuous, and 

 have a peculiar mode of branching. Single fibres extend radiatingly from 

 the corners of the stomach ; when about halfway to the surface of the body, 

 eavih fibre forks two or three times, and then one prong goes to each of the 

 two nearest longitudinal chymiferous tubes, and the third one extends to 

 the base of the deep tentacular socket. This is the general arrangement 

 at this age, although occasionally one of the prongs of the fork is absent 

 or only partially developed. Sometimes each prong forks again, at a 

 narrow or wide angle. From the tentacular sockets fibres extend also to 

 the surface midway between the mouth of the former and the adjacent 

 longitudinal chymiferous tube. So few are all the fibres, however, that 

 with a casual glance they might be mistaken for light unimportant streaks 

 here and there, instead of such methodically arranged bodies. 



