32 SUMMARY OF CURRENT RESEARCHES RELATING TO 



lateral folds which project from it. A slight posterior indentation 

 marks the anterior end of the future cell, which thus faces in an 

 opposite direction to that in which the embryo faces. 



Stage 4. Bounded Pentagon. — The two angular folds become 

 narrow and turn towards the top. The aboral face becomes united 

 by its edge with the quadrangular base ; its lower edge becomes 

 severed from the rest, and remains attached to the base, forming the 

 skin or wall which constitutes the future cell. The rest of the 

 plate still remains in contact with the ciliated zone, and forms a 

 broad ring, occupying, with the intestine, all the interior of the embryo. 

 A thickening appears internally, corresponding in position to the cap 

 on the outside, and forms the internal epithelial layer. The two 

 small lobes which originated from the ciliated aperture unite with 

 the pyriform organ, forming a thickening which is the origin of the 

 external muscular layer of the polype. 



Stage 5. Bedangular Oval. — Besides changing its shape, the 

 embryo has the cap and the internal epithelial rudiment pushed into 

 the interior ; the internal ring formed by the ciliated zone, &c., de- 

 generates, commencing with its internal part ; the pyriform organ also 

 degenerates. The external part of the internal ring assumes a horse- 

 shoe shape, and its protoplasm becomes granular. This, with the 

 epithelial and muscular rudiments, which come into contact by 

 growth, constitute the whole internal organization. 



Stage 6. Square Embryo. — The cells of the skin become distinct, 

 and secrete a cuticular envelope. The anterior part becomes divided 

 into two lobes by the union with the invagination-opening of the 

 indentation which forms the cell. 



Stage 7. Polyjnde icitli Primitive Peduncle. — The muscular has 

 entirely enveloi)ed the epithelial rudiment. The polype-rudiment 

 extends from the orifice of invagination to the base of the horseshoe. 

 The horseshoe is entirely composed of globules. The primitive cell- 

 cavity begins to disappear, and that end of the body in which it lies 

 becomes rounded. 



Stage 8. Stage of complete Degeneration. — The polype-rudiment 

 loses its connection with the horseshoe, and contracts into a round 

 mass suspended from the body-wall ; the invagination orifice closes. 

 The globules composing the horseshoe become scattered. The dis- 

 tinction between the orifice and lower surfaces of the cell becomes 

 more marked. 



Summing up the main deductions from these facts, the author 

 considers that Grant's theory of retrogi'ade development, as applied 

 to this case, must be abandoned. The development of the body and 

 its organs is uninterrupted from the egg to the adult, but its regu- 

 larity is disturbed by the loss of organs which occur in the larva, but 

 are not preserved in the adult. 



In its main features the development is meroblastic, although the 

 earliest period presents in the Escharines a truly holoblastic condition. 

 The intestine, as a coherent organ, is entirely wanting in the embryos 

 of Ectoprocta, by which point, as well as by the possession of a 

 mantle, they differ from the Entoprocta. A true mantle is represented 



