CTENOPHOR^. 13 



the Discophora;, with the full ex2)cctation 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 Medusa?. If the Discophora? are 

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

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

 the latter division including all the suborders of the Discophora? of 

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



The remarkaljle changes of form the Ctenophora? undergo until they 

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

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

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

 ciall}^ Avanting is an embryology of Cestum, which Avould give us, with 

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

 orders of Ctenophorte, a standard for an embryological classification of 

 the Ctenophora\ We can already see that many of the genera of 

 Eschscholtz {Medea and Pandora), as has already been suggested l)y 

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

 species as the CydijjjJe quadricostata of Sars {BoUna norvegica), the 

 Cyd'q^jye hrevicostata of Will (Chiaja niultkornls M. Edw.), and the 

 Slcyosoma rutUum of Gegenbaur, are undoul)tedly 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 

 transfoi'mations of Bolina alata, I should even be inclined to consider 

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

 of Euramphoia vexUIiffera Gegenb. It seems to me that there is be- 

 tween these two species the same I'elation which exists between some 

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

 mand is too impei'fect 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 PleuroI)rachia were 

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

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

 servations here presented, in the descriptions of oiu' common species, 

 were made independently during the summers of 18G0 - 03. 



