Budding in Perophora. 141 



completed, and when the folds which will cut off the peri- 

 branchial cavity are not very deep, the wall of the inner 

 vesicle far up on the left side at the extreme posterior end 

 becomes much thickened, and at once evaginates to produce a 

 little blind pouch, the rudiment of the digestive tract. This 

 lateral diverticulum grows out as a tube, which bends sharply 

 downward and forward, while through the displacement of 

 the vesicle its proximal end is carried up to the mid-dorsal 

 line. 



The tube very soon turns abruptly on itself to form a U, 

 and, now growing upward alotig the outer wall of the left 

 peribranchial sac until it reaches the dorsal surface, it there 

 bends directly forward, and stops short at the posterior wall 

 of the cloaca. Here a fusion takes place, and ^an opening 

 breaks through to form the anus. 



The differentiation into oesophagus, stomach, and intestine 

 is apparent at quite an early stage, and the whole tract, 

 which lies entirely on the left side of the bud, later becomes 

 closely enveloped by the outer wall of the peribranchial 

 cavity. 



The " pyloric gland," or " organe refringent " of Giard, 

 arises as a tubular diverticulum from the anterior wall of the 

 stomach, and produces a dichotomously branching system of 

 tubules, which form a lacework closely surrounding the intes- 

 tine. Each tubule terminates in a little vesicle or ampulla, 

 whose walls are made up of very flat cells containing deeply 

 staining nuclei. 



There is nothing in the structure of this organ to suggest 

 a glandular nature, but, as Pizon (/. c.) supposes, its function 

 is probably to absorb the products of digestion. 



The Pericardium and Heart. 



In sections of very young buds it is seen that many isolated 

 cells of a mesodermal appearance and exactly like the free 

 amoeboid cells of the blood are lying at numerous points 

 against the outer surface of the endoderm and inner surface of 

 the ectoderm. 



When the difference in thickness between the right side 

 and the rest of the inner vesicle is becoming apparent, a 

 marked tendency in these scattered cells to accumulate in one 

 spot is noticed. At first there is but a single layer of cells 

 joined loosely end to end, and forming an elongated patcii 

 adhering to the outer wall of the inner vesicle high up on the 

 right side in the posterior end of the bud. This is the rudi- 

 ment of the pericardium^ which is the first organ to make its 

 appearance. 



