252 



CTENOPHOR.^, 



Part II. 



of the month.- But the moment I placed the diameters of the two bodies in a po- 

 sition inverse to their length, all parts being placed in the same natural relation 

 as ftxr as they correspond by structure, their perfect homology, throughout the sys- 

 tem, was at once established. And not only the correspondence and antagonism 

 between the abactinal area and the tentacles, but also the minor details in the rami- 

 fications of the chymiferous system, agreed in every respect. The difficulty under 

 which I had labored was precisely that of an artist attempting in a family picture 

 to bring out the resemblance between two kindred faces, while contemplating one 

 individual in profile and the other in a front view, l)ut believing their position to 

 be the same. With this inverse relation between the homologous piirts, considered 

 in their reference to form in the two genera Bolina and Pleurobrachia, there is a 

 corresponding opposition between the natural positions of the two animals in the 

 surrounding medium. Pleurobrachia, as I have stated, swims naturally with the 

 mouth upward or forward, and the circumscribed area down^vard or backward ; Bo- 

 lina moves with the mouth downward and the aljactinal area upward. 



The position of the tentacles, their natural relations to the body when in motion, 

 and the direction of the aperture through which they issue, were the chief sources 

 of error Avhicli led me at first to consider them as difiercnt organs ; for in Pleuro- 

 brachia (PI. IP. Figs. 22, 23, and 25) they are turned toward the cadiac apertures, 

 while in Bollna {Figs. 88 and 89 iii) they are turned toward the oral aperture. But 

 now we may ascertain the homo- 

 logical identity of these appen- 

 dages, by placing these two ani- 

 mals in their normal position, in- 

 stead of viewing them in their 

 natural attitudes. And it will 

 be easy to understand how, in 

 accordance with the form and 

 movements of the various inem- 



a and / Long rows of locomotive fringes. - ]jQi-g yf tllC wliolo family, tllC 



j; and h Short rows of locomotive fringes. 



tentacles may issue from difler- 

 ent heights of the vertical di- 

 ameter upon the sides of the 

 body, and, according to the di- 

 rection of its movements, be bent 

 either toward the mouth or 

 toward the cadiac apertures. 

 Judging from Pleurobrachia and 

 Mertensia when contrasted with Bolina and Eurampha\a, we might infer that the 



Fuj. m. 



Bolina alata, Ag. 

 (Seen from the broad side.) 



— Central black speck (eye-speck). — 

 t to m Triangular digestive cavity. — i to o 

 Tunnel'like prolongation of the main cav- 

 ity. — V Chymiferous tube of the tenta- 

 cular apparatus. — vi Tentacular appa- 

 ratus on the side of the mouth. — rr Ear- 

 like lobes, or auricles, in the prolongation 

 of the short rows of locomotive fringes. 



— / 1 Prolongation of the vertical chymife- 

 rous tubes. — )i n The same tubes turning 

 upwards. — xx Bend of the same tubes. 



— ; z Extremity of the same tubes meet- 

 ing with those of the opposite side. — m 

 Recurrent tube anastomozing with those 

 of the auricles. 



Bolina alata, Ag. 

 (Seen from the narrow side.) 

 b Long rows of locomotive fringes. — ch 

 Short rows of locomotive fringes. — o Cen- 

 tral black speck (eje-speck). — i Upper 

 end of the digestive cavity. — i to o Fun- 

 nel-like prolongation of the main cavity of 

 the body. — vi to i Digestive cavity. — rr 

 Auricles. — in Mouth. — t t Prolong- 

 ation of the vertical chymiferous tubes. 

 — n n The same turning upwards. — xx 

 Bend of the same tubes. — z Anastomosis 

 of the two longitudinal tubes tt. — wiv 

 Recurrent tube, anastomozing with those 

 of the auricles. — A comparison of this fig- 

 ure with Fis;. 8S gives a distinct idea of the 

 relative position of the digestive cavity, ;« 

 to i, and the chymiferous tubes of the ten- 

 tacular apparatus v. 



