234 FOURTH REPORT — 1834. 



Since the appearance of Eschsholtz's work, three or four valu- 

 able memoirs have been published bydifferent observers in further 

 illustration of the Acalepha. One of these is a monograph on 

 the genus Diphya by Lesson*, containing several new remarks 

 on these animals. He thinks that many of the genera instituted 

 by Quoy and Gaimard are only separate pieces, or articulations, 

 detached from the aggregate mass of the animal which forms his 

 genus Plethosoma. A second is a memoir by Tilesius, published 

 in 1831f , in which are descriptions and figures of many species of 

 Meduscs, more particularly belonging to the genus Cassiopea, 

 accompanied by general remarks on this group. A third is a 

 paper byMilne Edwards on the structure of Carybda marsupialis, 

 in the Jinn, des Sci. for 1833 J ; and a fourth, one by Dr. Grant 

 on that of the Beroe P'deit^, published the same year§. These 

 last two memoirs, although treating only of single species, are 

 of importance as tending to raise our notions still further with 

 respect to the organization of these animals. The Carybda 

 marsupialis is a species belonging to that portion of the JHe- 

 dnsce which have been hitherto considered as having no stomach, 

 and in this and other respects, as possessing a structure even far 

 more simple than the rest of this family. Edwards has found 

 this to be erroneous, by tracing the existence not only of a sto- 

 mach and mouth, but of biliary ducts, as well as ovaries. He 

 shows that its structure is quite as complicated as that of anjf 

 other oi the Jledusce. Dr. Grant, in dissecting Beroe Pileus, has 

 discovered an arrangement of filaments and ganglia which, from 

 their general appearance and mode of distribution, he considers 

 as constituting a nervous system. This is a great step gained 

 in our knowledge of the structure of the Acalepha. Rosenthal 

 sought in vain for traces of a nervous system. Quoy and Gai- 

 mard, as well as many others, seem satisfied with respect to its 

 entire absence. Dr. Grant however observes, that although 

 nerves have not hitherto been shown in the Acalepha, he thinks 

 they will be found even in the simpler forms of Medusce, which 

 he has shown elsewhere to be afl:ected by light, as well as 

 Actinice, HydrcB, and Furcocercce, 



An important work was published by Blainville in 1830, in 

 which he has embodied a vast deal of information relating to the 

 structure, history, and classification, not only of the present 

 tribes, but of all the other animals belonging to Cuvier's divi- 



• Published in his Centurie Zoolog. Nov. 1830. 



f Nov. Act. ^-c. Nat. Cur., torn. xv. p. 247. X toni. xxviii. p. 249. 



§ Zool. Trans., vol. i. p. 9. 



