CTENOPHOR^E. 13 



the Discophoroe, with the full expectation that future researches will 

 give us better reasons than we have at present for abandoning, as con- 

 trary to nature, two orders which have thus far been almost universally 

 acknowledged by all investigators of Medusae. If the Discophorae are 

 to be united with the Hydroids, we shall have to divide the Acalephs 

 into two orders, Ctenophorae and Medusidae ; the different suborders of 

 the latter division including all the suborders of the Discophorre of 

 Eschscholtz, and those of the Hydroids as limited by Professor Agassiz. 



The remarkable changes of form the Ctenophorae undergo until they 

 attain their adult state, will necessitate at no very distant time a com- 

 plete revision of the Ctenophorse, as soon as the embryology of a suffi- 

 cient number of families has become well known. What is now espe- 

 cially wanting is an embryology of Cestum, which would give us, with 

 what has been shown here of the embryology of the three other sub- 

 orders of Ctenophorse, a standard for an embryological classification of 

 the Ctenophorre. We can already see that many of the genera of 

 Eschscholtz (Medea and Pandora], as has already been suggested by 

 Professor Agassiz and by McCrady, are only embryonic stages ; all such 

 species as the Cijdippe qiiadricostata of Sars (BoUna norvegica), the 

 Cydl-ppe brevicostata of Will (Ckiaja multicornis M. Edw.), and the 

 Sicyosoma rutilum of Gegenbaur, are undoubtedly undeveloped stages 

 of some of the well-known Ctenophorce of the Northern Ocean, the 

 Adriatic, and the Mediterranean. From what has been shown of the 

 transformations of Bolma alata, I should even be inclined to consider 

 the Cydippe hormiphora of Gegenbaur as one of the stages of growth 

 of Euramphaxi vexiUigera Gegenb. It seems to me that there is be- 

 tween these two species the same relation which exists between some 

 of the stages here figured of Bolma alata. The material at my com- 

 mand is too imperfect to attempt anything more definite than the few 

 hints here thrown out for more fortunate observers. 



Professor Agassiz, in his third volume of the Contributions, intended 

 to give an embryology of some of our species of Ctenophora?. He 

 made many observations previous to 1856, which, however, were never 

 noted down ; only a couple of sketches of a young Pleurobrachia were 

 drawn by Mr. Sonrel ; and during the subsequent summers other and 

 more pressing work compelled him to forego his intentions. The ob- 

 servations here presented, in the descriptions of our common species, 

 were made independently during the summers of 1860 - 63. 



