Chap. I. SUB-ORDERS OF CTENOPHORiE. 177 



This once settled, it remains to Ije seen how many such sub-orders there are among 

 Ctenophor;\?, and Avhat is the range of their structural peculiarities, and next to 

 ascertain in the same way the number and natural limits of the families in each 

 of these natural groups. 



As Gegenljaur has already noticed, Leuckart has based his primary subdivisions 

 of the Ctenophoi'a3 upon a character of comparatively little value, — the dimensions 

 of the digestive cavity. It is nevertheless true, that the group thus separated 

 from the (jther types under the name Eurystomata is a very natural one, already 

 distinguished by Eschscholtz, to whose family of Beroidae it exactly corresponds, 

 as well as to Gegenbaur's third group of Ctenophora^, without lobes and without 

 tentacles. There is therefore no discre23ancy among naturalists as to the existence 

 of a natural division among Ctenophora?, including the species most closely allied 

 to the genus Beroe of Brown. Eschscholtz recognizes it as a family luider the 

 name of Beroid* ; Mertens as a family under the name of Idya ; Lesson as a 

 tribe under the name of Beroie ; Leuckart as an order under the name of Eu- 

 rystomata; and Gegenbaur as one j^rin^f^ry division of the Ctenophorce including 

 the only family of Beroida^. But while all agree upon the limits of that group 

 of Acalephs, there is the widest discrepancy among them as to its rank and 

 standing in the class. 



Li attempting to decide between these conflicting opinions, it must be Jjorne 

 in mind, that, in analyzing the characteristic features of these Beroids, we have to 

 consider different categoiies of characters. In the first place, the Beroe proper 

 have all those structural peculiarities in common with the other Ctenophora?, which, 

 from their complication, place them highest in the class of Acalephs as a distinct 

 order. But, though agreeing with the CtenophorfB generally in the complication 

 of their structure, they difler from all other Ctenophora; in one striking anatomical 

 character, entirely independent of their peculiar form, — ilioj have no infercmibulacral 

 chjmifcrovs tube, which exists in all others. The existence of two parallel chy- 

 miferous tubes in the transverse plane of some Ctenophoroe, on lioth sides of the 

 digestive cavity, was first pointed out by Milne-Edwards in his admirahle description 

 of LeSueuria vitrea (Ann. Sc. Nat. 2" ser. vol. 16, p. 203, PL 3, Fir/. 1 h and /). 

 Will has described them in Eucharis multicornis (Horaj tergestina, p. 31, PI. I. 

 Fi(f. 3, b and c). I myself have traced them in Bolina (Mem. Am. Ac. IV. PI. 7, 

 Fiffs. 4, 7, and 8). Gegenbaur, however, mentions and figures only one of them. 

 As they are easily confounded, on account of their parallel course, I have no doubt 

 that he must have confounded them. One is deeply seated, close to the digestive 

 cavity, and communicates Avith the tube encircling the mouth ; the other is more 

 superficial, and quite at the surface, near the mouth. They are best seen facing 

 the anterior or the posterior surface of the animal, as their divergence is thus 



VOL. in. 23 



