286 CTENOPIIORiE. Part U. 



of the Ctenophoi';i3 is a Cyclopean structure, resulting from tlie central combination 

 of the sevoi-al ej'e-specks occupying in other types of the class a peri2:)heric ])osition 

 at the end of the ambulacral zones. The whole structure of Eatliates, however, is 

 so remote from that of the other l)ranches of the animal kingdom, that any attempt 

 to homologize their functions beyond the respective limits of the j^rimary types is 

 more likely to lead to errors tlian to explain their peculiarities. 



Having thus described our Id_yia, the question now arises, What are its specific 

 characters ? for, if the views I have advocated in tlie first part of this work are at 

 all well founded, it must be obvious that I have embraced in this description many 

 features which are in no way specific. The fundamental structure of our Idyia, 

 as composed of eight spheromeres, is not a specific character, since it is common 

 to all the Ctenophora) ; nor are the ec[ual)le development of the spheromeres and 

 the ramifications of the ambulacral tubes specific characters, since all the true Beroids 

 agree in this respect ; nor is the aljseuce of tentacular tubes and of tentacles a 

 specific character, since no member of this sub-order has them ; nor is the great 

 width of the digestive cavity, nor the limited extent of the main cliymiferous cavity, 

 specific, since all the Beroids agree in the development of these parts ; nor is the 

 structure of the ovaries and spermaries, nor that of the circumscribed area. But, 

 instead of enumerating anew all the structural details mentioned in this section, 

 I may as well at once express my conviction, that no structural peculiarity can 

 ever )je considered as a specific character, since the essence of S2:)ecies does not 

 lie in the plan of structure, nor in its mode of execution, nor in its complication, 

 nor in the combinations which determine the form, nor even in the details of 

 the structure. These categories of structure determine respectively the branches, the 

 classes, the orders, the fiimilies, and the genera of the animal kingdom ; Avhile the 

 species* are characterized l:)y their size, the relative proportions of their parts, their 

 ornamentation, their geographical range, their relation to the elements in which they 

 live, their mode of existence, the duration of their life, their association with one 

 another, the period of their reprt)duction, tlie changes they imdergo during their 

 life, and their association with other Ix'ings. Considering, now, our Idyia in this 

 light, I may say that its most strils:ing specific peculiarities are its great size ; the 

 prominence of its vertical diameter ; its equable and gradual widening from the 

 abactinal pole toward its middle height, and its still more gradual tapering toward 

 the mouth ; its light rosy color, intensified with age, and particularly bright about 

 the sexual organs, and deep pink upon the spermaries during the season of spawning, 

 the color groAving deeper in consequence of the accumulation of pigment cells. 

 This species lives along the coasts of New England, and northward : it is found 

 near the shores, and, though sometimes ajjpearing in immense numbers, it cannot 

 l)e said to lead a gregarious life and to form shoals, as they do not move together, 



