CNIDARIA 



107 



and thus the former anterior end becomes the foot of the 

 scjphopoljp ; this soon contracts a little, whereas the 

 posterior end widens, so that in this way the body acquires 

 the goblet shape characteristic of polyps (Fig. 52 B). 

 During the attachment a cement, which soon hardens into a 

 plate with upturned margins (Figs. 54 and 55 k), is secreted 

 from the foot. The secretion of a mesogloea begins early 

 between the two layers of the larva (Fig. 52 B, g). 



The next change is the formation of the permanent month, 

 which arises by a process of invagination. The ectodermal 

 layer of the prostomal pole invaginates into a gradually 

 deepening ectodermal pocket (Fig. 52 B, s), at the bottom of 

 which a perforation, leading into the gastral cavity, soon 

 arises. In this way an oesophagus, lined with ectoderm, is 

 produced (Fig. 52 (?) ; the outer opening is known as the 

 mouth, the inner, communicating with the gasti'al cavity, as 

 the inner opening of the oesophagus (Fig. 52 C, sp). By means 

 of this process of invagination the entodermal sac becomes 

 crowded downwards, but not thi-oughout its entire extent. 

 Since the larva is compressed laterally, two glove-like ento- 

 dermal processes, corresponding in position to the long'er of 

 the secondary axes, ai'e preserved. These project upward, 

 and are the first two gastral pouches (Fig. 52 G m and D m). 

 Very soon, however, in a plane at right angles to this, a second 

 pair of gastral pouches grows upward as diverticulte of the 

 central stomach (Fig. 52 E), so that now the radiate type 

 with four rays is reached. We now have an oesophagus 

 invaginated from the ectoderm, in the circumference of 

 which, at the four radii, lie gastral pouches in connection 

 with the gastral cavity.^ At these places, where two neigh- 

 bouring gastral pouches come in contact, a partition, or 



1 [Our knowledge of the first processes of development in the Scyphis- 

 toma stage has been materially increased by recent investigations, which 

 have advanced information in several directions. Nevertheless it is not 

 possible as yet to pronounce final decision concerning these develop- 

 mental processes. The observations of Goette have been only partially 

 confirmed by Glaus (Nos. I. and II., Appendix to Literature on Scypho- 

 medusffi). As the result of his most recent observations, Claus (No. II.) 

 denies totally the presence of an ectodermal pharynx. Of special import- 

 ance are the statements of Claus (No. II.) concerning the formation of 



