OF THE ROTATORIA. 469 



cannot be adduced as a law, that the highly developed nervous system of the 

 hio-her forms is an essential character of the Crustacea. 



" The mode of termination of the sensitive nerves is that seen in Crustacea 

 and Insecta ; but the like is not kno^vn among Vermes. Ehrenberg pointed 

 out the similarity of the eye-specks to those of Crustacea. The several seg- 

 ments and texture of the ahmentary canal afford no decisive evidence, since 

 many Vermes have horny jaws, as have the Eotifera. The masticatory 

 apparatus of the young Daphmce presents a pretty close resemblance with 

 that of Rotatoria — the two opposed jaws expanding into a plate toothed with 

 numerous transverse ridges, like those of Lacinularia. The stomach-glands 

 probably have their analogues in the lobed glandular appendages — the so- 

 called ' salivary glands ' of Cirripedia. 



" Similar organs, however, exist in many dorsibranchiate Vermes ; and like- 

 ^vise in many Vermes and lower Crustacea the liver is represented by large 

 cells with peculiar contents, situated in the walls of the stomach and intes- 

 tine. The absence of an intestine in a few Rotifera may appear opposed to 

 their Arthropodous type ; yet in the Neiu'opterous larva of Myrmeleo the 

 faeces are discharged by the mouth, and the rectum itself is transformed into 

 a spinning organ. Moreover, the intestinal canal of many Eotifera, e. g. 

 Eucldcmis and StejjJianoceros, recalls, in its peculiar bell-hke movement, the 

 exactly similar character of the intestine of certain parasitic Crustacea 

 {Achtheres, Tracheliastes, &c.). 



'" The substance regarded as urinarj- concretions is evidently closely re- 

 lated to that formed in the larva of Ci/cloj^s ; but no such j)oint of resemblance 

 is found among Vermes. 



" Lastly, the anatomical and physiological phenomena of sexual life greatly 

 favour the Crustacean relationship. Several minor particulars may be alluded 

 to — such as the j)roduction of two kinds of ova (indeed the winter ova of 

 Tr'iarthra have a great hkeness in the construction of the shell with the 

 ephippial ova of Daj^hnia), the fact that many species cany their eggs about 

 with them (although it is tnie the same is seen among Vermes, for instance 

 Clepsine), and the occurrence of coloured oil- corpuscles in the yelk of not a 

 few Rotatoria — all indicating a Crustacean type. The striking analogy be- 

 tween the male (in some sense aborted) Rotatoria and the males of many 

 Cnistacea is one of far higher import. It is only necessary to call to mind the 

 diminutive parasitic males Nordmann discovered in the females of Achtheres, 

 BrachieUa, Chondracanthus, and Anchorella, and such as Kroyer foimd in 

 other Lernceopoda and Lerncece. 



^' Moreover, the embryonic histoiy of Rotifera is in favom^ of the alHance, 

 — viz. the imperfect development of the young of several species, on their 

 emergence from the egg, and the necessary metamorphosis they undergo 

 before attaining the adult condition. Lastly, the diminution or even com- 

 plete disappearance of the eyes after birth fiu-ther indicates an analogy with 

 certain Crustacean forms. 



" ^\Tiilst the foregoing considerations approximate the Rotifers to the 

 Crustacea, the nature of the resj^iratory apparatus and the presence of the 

 yibratile ciHa separate the two, and assimilate the Rotatoria to Vermes ; yet 

 in both these particulars they make an equal approach to Echinodermata, 

 inasmuch as the pecuhar vibratile organs of Synajyta du/itata appear to be 

 similar structures with the vibrating organs (tags or gills)." 



Now, argues Ley dig, it seems but just to allow the sum of the resem- 

 blances to any class, if greater than that of the differences, to determine the 

 systematic position. If this be granted, as the sum of resemblances of the 

 Rolifera with the Crustaceans seems assuredly greater than that of their 



