CTENOPHOR^. 13 



the Discoplionu, with the lull 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 l)een almost universally 

 acknowledged by all investigators of Medusa'. If the Disco])hora3 are 

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

 into two orders, Ctenophora? and Medusida} ; the different suborders of 

 the latter division including all the suborders of the Discophone of 

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



The remarkable changes of form tlie Ctenophori\3 inidergo until they 

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

 plete revision of the Ctenophora), as soon as the embryolog}^ of a suffi- 

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

 cially wanting is an end^ryology of Cestum, which woidd give us, with 

 what has been shown here of the embryology of the tliree other suIj- 

 orders of Ctenophon\^, a standard for an embryological classification of 

 the Ctenophora3. We can already see that many of the genera of 

 Eschscholtz {Medea and Pandora), as has already Ijeen suggested by 

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

 species as the Cyd'ipiie qiiadricostata of Sars [Bolina norvegica), the 

 Cydippe hrevkostata of Will (Chlaja midtlcornis M. Edw.), and the 

 Stcyosoma rutilum of Gegenbaur, are undoubtedly undeveloped stages 

 of some of the well-known Ctenophora? of the Northern Ocean, the 

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

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

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

 of Euramphcea vexillicjera 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 Bolina alata. The material at ni}^ com- 

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

 hints here thrown out for more fortunate ol^servers. 



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

 to give an embryology of some of our species of Ctenophora3. He 

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

 noted dowm ; only a couple of sketches of a young Pleurobrachia Avere 

 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 dmiug the summers of 1860-63. 



