198 CTENOPIIOR.^. Part II. 



has mi.staken the base of the tentacles for ovaries. To this family lielong the 

 genera Mertensia Less. (Beroe eompressa 3Iert.), Owenia KolL, Gegenljaiuia Ag. 

 (Eschsclioltzia eordata Koll.), and Martensia Aff. (Beroe octoptera Ileri.). 



We have thus three families of the Ctenophoraj Saccatte : the Callianirid.e, 

 the Cvini'i'iii.E proper, and the Mertensid.e, the first of which is still very im- 

 perfectly known. 



Cestiu.e. Whether the genus Cestum constitutes a sub-order b}^ itself or not, 

 it is unquestionably the type of a distinct family, for which the names Cestoidece 

 and Cestida^ have been proposed Ijy Lesson and by CfCgenljaur. These names are 

 objectionable so far as they resemble too much that of the Helminths called 

 Cestoidea, and a mere grammatical difference in the termination of a systematic 

 name hardly constitutes a satisfactory distinction. Eschscholtz united Cestum wdth 

 Cydippe and Callianira; but, leaving the peculiar arrangement of the rows of loco- 

 motive flappers out of consideration, the tendency of the Cydippida?, and especially 

 of the Mertensido}, to elongate in the direction of the transverse or diacoehac 

 diameter, while in the Cestida^ the prominent diameter is the longitudinal or coeliac 

 diameter, seems to indicate different affinities and a closer relation to the Cte- 

 noi3hora3 Lobata\ This relation seems further supported by the position and 

 termination of the tentacular apparatus, which trends in the direction of the coeliac 

 cavity, and protrudes on the sides of the actinostome, and not in the direction of 

 the a))actinal pole, as in the Cydippida^ and Mertensida'. It is true, McCrady has 

 noticed that a change in the direction of the tentacular tubes takes place with 

 the growth of Bolina ; Ijut this does not militate agamst the importance of the 

 course of the tentacular apparatus in adult Ctenophora\, since in all the Loljatfe 

 known it protrudes from the sides of the actinostome in their adult state, and in all 

 the Saccata3 examined with reference to this point its opening is turned towards 

 the abactinal jjole. Among the less known species, Cydippe dimidiata Esch., and 

 Beroe glandiformis Mcrt., are the only ones in which it is represented as trending 

 in the opposite direction. But Grant also represents that of Beroe Pileus as 

 trending in the direction of the mouth, when its real position is certainly the 

 reverse. We ma}', therefore, well consider the direction of the tentacles as char- 

 acteristic of the sub-order of the CtenophortB Saccatas and Lolxata ; and, making- 

 due allowance for the possibility of mistakes with reference to a structural feature 

 thus far not sufficiently noticed among the characters of these animals, allow it its 

 due weight in the estimation of the affinities of Cestum. 



If I am not greatly mistaken, the singular animal described by Gcgenl_)aur as 

 a distinct genus, under the name of Sicyosoma, is a 3"oung Cestum ; for Avhat he 

 takes to be the ovaries reminds me rather of the remnants of the yolk of an egg. 

 When it is remembered that Cestum is the largest of all the Ctenophora, and 



