ACALEPH^E. 117 



1. 1804, p. 134, PL vi. fig. 3, A, B, C. The two pieces provided with 

 swimming cavities, nearly similar in form, were afterwards, by 

 CUVIER (Eegne Anim. sec. ed. in. p. 288) and other writers, 

 erroneously taken to be two animals which had become attached 

 to each other, an opinion occasioned by observing that they 

 were readily separated. This separation, or spontaneous detach- 

 ment of different parts, has often been remarked in the entire 

 order as in Physsophora, Ehizophysa, Stephanomia. In fact, 

 Diphyes is much more nearly allied to these genera than might 

 be suspected from many, and sometimes very confused, descriptions 

 of it. I may remark, that the part which, in our description, 

 we have indicated as anterior, is called posterior by the first 

 discoverer, BOEY, and by many others after him. 



QUOY and GAIMARD, who discovered many new species of this 

 family and formed new genera from them, (Ann. des Sc. nat. 

 Tom. x. 1827, p. 5 21,) determined subsequently to bring them 

 all under the single genus Diphyes, (Voyage de decouvertes de 

 I' Astrolabe, Zoolog. Tom. iv. 1833, p. 81). [But more accurate 

 observations of late years have shewn that this proceeding is not 

 advisable. In Praya the swimming bells are similar in form, 

 and are placed, more or less, side by side, and their cavities 

 open on opposite sides of the stem. In Diphyes the bells are 

 placed behind one another and open backwards. 



The common stem begins within the substance of the anterior 

 bell, or piece, in a more expanded portion, which is lined with 

 large epithelial cells, and has very different form in different genera. 

 This expanded portion often contains a globule of oily matter. 

 Beneath it the stem gives origin to the canals of the swimming 

 pieces, and then is prolonged to become the common axis of the 

 colony. 



The polyps with their different appendages are fixed to the stem 

 at regular intervals. Those nearest to the swimming pieces are 

 quite undeveloped and without appendages. Those at the other 

 extremity of the stem are the oldest and most perfect, and have 

 their appendages most complete. Each group consists of a Polyp, 

 a set of prehensile organs, and the generative organ, which partakes 

 more or less of the medusan form the whole being covered by 

 a protecting bract. Such a group either persists in adhering to the 

 common stem, (Diphyes, Praya), and then only certain parts are 

 detached, as the medusiform capsules of the sexual organs ; or it is 



