Chap. IL 



LIMITS OF THE CLASS. 



communities of free-moving gelatinous animals, the 8iplionopliora3 {F!g. o), Avliich 

 others consider as genuine Acalephs, while some do not hesitate to unite all 

 Acalephs and Polyps in one single division. On the other 

 hand, we have lately seen a part of the Acalephs, the Cteno- 

 phora3 {Figs. 4, 5, 6, and 7), removed from that class, and 

 referred to the type of MoUusks. 



Such conflicting views could not he entertained by so 

 many and such eminent naturalists, did not almost insuper- 

 able difficulties obstruct our attempts to trace the truth. I 

 know only one way to overcome these obstacles, and to attain 

 greater precision on this subject. It is to test the affinities 

 of all these animals by the standard of what is known of their 

 mode of development, in the manner done before with full 

 success for other classes ; taking at the same time into account the homologies of 

 their parts, as far as they can be ascertained. Embryology has, indeed, become 



Young Physophora, 

 {Copied from Gegenbaiier.) 

 Buds of swimming bells. — bb So- 

 called tcntaclfs ; lower 6 so called 

 Polyp. ~ c r Fi'ck'rs with lasso 

 cells. — r Air sac. 



Fiff. 4. 



Fiff. 5. 



Fig. 6. 



BOLINA ALATA, Ag. 



{Seen from the broad side.) 



a and / Long rows of locomotive fringes. — 



g and h Short, rows of locomotive fringes. 



— o Central black speck (eye-speck?). — 

 1 to m Triangular digestive cavity. — r to o 

 Funnel-like prolongation of the main cav- 

 ity. — V Chymiferous tube of the tenta- 

 cular apparatus. — m Tentacular appa- 

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

 like lobe, or auricles, in the prolongation 

 of the short rows of locomotive fringes. 



— ( t Prolongation of the vertical chymife- 

 rous tubes. — n n The same tubes turning 

 upwards. — xx Bend of the same tubes. 



— z z Extremity of the same tubes meet- 

 ing with those of the opposite side. — w 

 Recurrent tube anastomozing Tvith those 

 of the auricles. 



BOLISA ALATA, Ag. 



(Seen from the narrow side.) 

 lb Long rows of locomotive fringes. — ch 

 Short rows of locomotive fringes. — o Cen- 

 tral black speck (eye speck?). — (^ Upper 

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

 nel-like prolongation of the main cavity of 

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

 Auricles. — «i Mouth. — t t Prolong- 

 ation of the vertical chymiferous tubes. 

 — ji n The same turning upwards. — xx 

 Bend of the same tubes. — z Anastomosis 

 of the two longitudinal tubes tt.—ivw 

 Recurrent tube, anastomozing with those 

 of the auricles. — A comparison of this fig- 

 ure with Fis:- 4 gives a distinct idea of the 

 relative position of the digestive cavity m 

 to T, and the chymiferous tubes of the ten- 

 tacular apparatus v. 



BOLINA ALATA, Ag. 



(Seen from above.) 

 I Central black speck (eye speck?). — a be/ 

 Long rows of locomotive fringes. — cdgh 

 Short rows of locomotive fringes. — rr 

 Auricles. — 5s Circumscribed area of the 

 upper end of the body. 



BOLINA ALATA, Ag. 



(Seen from below.) 

 n Mouth, ^rt Auricles. — tttt Prolonga- 

 tion of the vertical chymiferous tubes. — 

 z z Anastomosis of these tubes. 



the key-note to the knowledge of the closer affinities among animals. Granting, 

 for instance, that anatomy alone could have settled the question of the true affini- 

 ties of the Barnacles with Crustaceans, I hardly believe, that, but for our knowledge 

 of their embryology, naturalists would ever have dared to consider them merely 

 as a group of the natural division of Entomostraca, which they really are. But 

 for our knowledge of the mode of development of toads and frog.s, their close 



