Chap. in. GENUS BOLINA. 251 



the circulation for a sufficient time to follow the entire course of the chymiferous 

 fluids within the body, throughout all its parts. Besides, being already minutely 

 acquainted with the arrangement of the chymiferous tubes in Pleurobrachia, I was 

 fully prepared to institute a minute comparison between the two genera, to ascer- 

 tain their differences, and to recognize the homology of their structure. I was even 

 able to trace the connection of all the jsarts of the chymiferous system so fully 

 in Bolina that I could ascertain the natural connections between all its peripheric 

 tubes and the central chymiferous cavity, as well as the peripheric anastomoses of 

 the tubes themselves. Such anastomoses are entirely wanting in Pleurobrachia, in 

 which the ambulacral tubes end in blind sacs, on the actinal as well as the abactinal 

 side of the body. Milne-Edwards presses too fir the typical identity of the chymife- 

 rous system in Ctenophorae. Had he perceived that these Acalephs, instead of form- 

 ing one natural family, constitute four sub-orders with many distinct famihes, he 

 would, no doubt, have given more weight to the differences which he himself has 

 observed in their chymiferous system, and of which he makes too light. 



In order fully to understand the structure of Bolina alata,^ and the relations 

 of its various parts, it is necessary first to have a precise idea of its external 

 form, which it is by no means easy to acquire, even after repeated investigations. 

 Like Pleurobrachia, the body of Bolina is more or less ovate, but in an inverse 

 direction ; for its greater diameter follows the jjlfine of the corresponding organs 

 in such a connection as to show that the antero-posterior diameter is the longer, 

 while it is the shorter in Pleurobrachia, and vice versa that the transverse diameter 

 is the shorter, while it is the greater in Pleurobrachia. This inverse agreement 

 between the natural relations of the organs and the external form is most satis- 

 factorily ascei'tained, upon comj^aring the position and direction of the circumscribed 

 area and of the tentacles ; and we shall hereafter see that the ^proportions of the 

 body with reference to their longitudinal and transverse develo^iment are in every 

 respect reversed in the two genera. Before this contrast had been established, I 

 was unable to trace the homology of parts between the two genera. Indeed, taking 

 the general form as a guide, I began by comparing the two animals in a position 

 in which I undertook to place their prominent diameters in the same relation, 

 and thus arrived at the conclusion, that the tentacles of Bolina, which are far less 

 developed and issue from the margin of the mouth itself, were organs entirely dif- 

 ferent from the tentacles of Pleurobrachia. The latter I considered as a system pe- 

 culiar to this type of Ctenophorae, because they are protruded from the sides of the 

 body ; while the tentacles of the type of Bolina appeared to me as a sort of fringes 



^ As I Lave published numerous views of this Academy, I would refer to them for further com- 

 animal, in different attitudes, in my paper on Beroid parisons, having only reproduced a few of them in 

 Medusaj, printed in the Memoirs of the American the wood-cuts of the following pages. 



