168 CTENOPHOR^. Part II. 



l^reseiitly, tliat the lasso cells of the tentacles of the Cteno^ihorte differ also greatly 

 from those of the Discophora\ I shall take occasion to consider more minutely the 

 direction of the sac containing these interamhulacral tentacles, when describing the 

 Cydip^^idas in detail. The homologies of the whole ch^miferous system of the 

 Ctenophora3 and Discophora) being thus fully established, it would he idle to 

 animadvert further upon the comparisons which have been made between the 

 Ctenoj)hora} and Tunicata : their resemblance is merely analogical. There is, how- 

 ever, one point in the structure of the Ctenophora>, which, in this connection, 

 deserves further consideration. 



I have already alluded to the homology of the whole chymiferous system of 

 the Acalephs, and the ambulacral system of the Echinoderms. A careful study of 

 this homology may throw some additional light upon the true nature of tlie black 

 speck in the centime of the circumscribed area of the CtenoiDhorae, and upon the 

 significance of the area itself Remembering that the eye-sj^ecks, or whatever the 

 organs at the peripheric end of the ambulacral zones of the Echinodemis may be, 

 are placed at the tip of the rays in the Star-fishes, and in the Sea-urchins on 

 the abactinal side of the spherosome, alternating with the ovarial plates ; rememl^er- 

 ing, further, that similar sensitive specks are placed at the tip of the ambulacral 

 chymiferous tubes in the Discophoraj, while there is but one such speck in the 

 centre of the axial prolongation of the funnel in the Ctenophora?, — the conclusion 

 seems unavoidable, that the broad expansion of the abactinal surface of the Dis- 

 cophora3 corresponds to the broad field occupied by the dorsal surface of the Star- 

 fishes, and that therefore the eye-specks of the Discophora} are not only homologous 

 to the eye-specks of the Star-fishes, but also occupy a homological j^osition in 

 the periphex'y of the spherosome, while in Ctenophora^ the single eye-speck has 

 a homological position with the five eye-sj^ecks of the Sea-iu'chins at the abactinal 

 pole of the spherosome, with this additional peculiarity, that in Ctenojjhora; there 

 is but one single eye-speck, and that there are five in the Sea-urchins. Such a 

 Cyclops-like fusion of the eyes occurs in other types of the animal kingdom, and 

 is not unfrequent in the Crustacea ; it cannot be an objection, therefore, to such 

 a homology. Moreover, the single eye-speck of the Ctenophora^ is closely connected 

 Avith the chymiferous system, as the many eye-specks are in the Discophorre and 

 Echinoderms ; and that connection, in accordance with the central position of the 

 eye-speck, takes place in the axial prolongation of the system. 



Whether these sensitive specks are to be considered as eye-specks, or as auditory 

 organs. Is another question, which also requires our consideration. Strictly siieaking, 

 they are not homologous to either eyes or ears, if the mode of develoj^ment of 

 these organs of the senses in Vertebrates is considered ; nor can they be com- 

 pared to the eyes or eai's of the Articidates, since in the former the higher organs 



