BIGELOW: THE CTENOPHORES. 395 



In an older stage of 20 mm. very similar to one shown by Mayer 

 (:12, pi. 5, fig. 19) the lappets have grown longer, the lappet-canals 

 already show the main loops of the adult, the tentacles now open at 

 about the level of the mouth, though their canals still lie far from the 

 oesophagus, and the young auricles are visible. The only apparent 

 difference between these specimens and infundibulum of correspond- 

 ing ages is that in the former the auricles appear before the lappet- 

 canals are fullv formed, whereas in the latter the reverse is the case. 



CESTIDA. 



CESTIDAE Gegenbaur. 



Cestum Lesueur. 



Up to the present time two species of Cestum have been described 

 from the Pacific, C. najadis Eschscholtz, and C. amphitrites Mertens; 

 but of neither is the status satisfactorily determined. Cestum najadis 

 is distinguished from the Atlantic veneris by its possession of long 

 tentacles of the cydippid type; and, according to Moser (: 08a, p. 13), 

 by its geographical occurrence. The latter reason can not be aban- 

 doned too soon, as I have already pointed out ( : 09) for similar cases 

 among Medusae; but the former is of real value, if it can be depended 

 upon. Unfortunately the animal is known from the original descrip- 

 tion only. And it would be so remarkable for a cestid to have long 

 tentacles, that we may be pardoned if we hesitate to accept the account 

 until it is verified. There is another difference between najadis and 

 veneris which has not been emphasized previously, namely that the 

 tentacle-bases are yellow in the former, colorless in the latter. In 

 this respect najadis agrees with amphitrites, but here again we are 

 confronted by the question of the structure of its tentacles. 



Cestum amphitrites was so beautifully figured by Mertens ('33) that 

 we can gain a very good idea both of its anatomy and of its general 

 appearance in life. Color proves a very obvious difference between it 

 and veneris, for whereas the latter is colorless, the tentacular bases of 

 the former are brownish yellow, and there is a spot of the same color 

 at either extremity of the band-like body. Anatomical differences 

 were thought to exist by Mertens ('33, p. 493) namely the presence 

 of "zwei Blattchen die das Stigma. . . .einfassen" and of "zwei band- 

 f ormige Kan ten .... die an beiden Flachen, der oberen wie der untern, 



