Haddon — The Netvly-Hatched Larva of Enphyllia. 131 



"While the embryo is still solid, the oesophageal invagination 

 makes its appearance. At this stage it swims feebly about, the 

 cilia having commenced to develop. 



The permanent endoderm is formed from the larval endoderm 

 by a differentiation of a peripheral layer from the central portion. 

 The CBsophageal invagination is much dilated at its base. Here 

 the ectoderm has preserved its intimate connexion with the 

 endoderm, the ectoderm cells not even having acquired a smooth 

 bounding surface. In the next stage this even surface has been 

 acquired, but at no time is a supporting lamella secreted over this 

 area. The absence of the lamella clearly facilitates the absorption 

 by the endoderm (or yolk) of the base of the invagination. The 

 central portion of the larval endoderm remains as food yolk. By 

 the time the layers are definitely established the yolk is a loose 

 mass of vesicles, the shells of which have begun to disintegrate. 



The supporting layer appears as a delicate membrane between 

 the two layers, and is not formed by the direct metamorphosis of 

 the ends of the ectoderm or endoderm cells. In later stages it is 

 found in places where it can only be endodermic, and in others 

 where it is evidently ectodermic. I am quite sure that in Mani- 

 cina it is formed as a cuticular secretion. 



To form the first mesentery the whole cesophagus moves 

 laterally, until in the meridian of the mesentery there is only sup- 

 porting lamella between the oesophageal and surface ectoderm. 

 The oesophagus now grows downward in the meridian as a lobe of 

 the ectoderm, which represents the primary filament, and which 

 pushes the endoderm before it. 



On the opposite side of the animal, along the line of the second 

 mesentery, the oesophagus became applied to the ectoderm in tiie 

 same manner, and a lobe grows down from it to form the second 

 filament. The mesenteries, as such, are formed by the ingrowth 

 of the endoderm between the body ectoderm and cesophagus 

 above, and between the body ectoderm and the filaments below. 



The primary pair of intermesenterial chambers is at first solid. 

 The larger chamber acquires its cavity before the smaller, the 

 excavation travelling from the lip of the oesophagus upward and 

 from the first toward the second mesentery. The excavation of the 

 primary chamber is closely followed by the reflection of ectoderm 



