CASSIOPEA XAMACHANA. 215 



together and coarsely granular at the proximal or posterior end of the larva. Toward 

 the equator the cells become higher ; and at the distal, or anterior, end they are large and 

 clear. The character of the endoderm makes it possible to identify the anterior end of 

 the swimming larva with the distal end of the bud. 



The Formation of the Mouth. The first change to be seen in the swimming larva 

 is the formation of the mouth, which occurs two or three days after the larva has been set 

 free. When writing my preliminary paper ('92 a) , I was in doubt as to the relation 

 between the poles of the bud and those of the larva. The better and more abundant 

 material obtained during the second visit to Jamaica proved conclusively that the proxi- 

 mal end of the bud forms the oral end of the larva, just as it does in Cotylorhiza, accord- 

 ing to Goette. The identification is made easy by the polar differentiation of the 

 endoderm described in the previous section. 



When first seen the mouth looks like a minute pin-hole in the posterior end of the 

 larva (m, Fig. 4 B) . In longitudinal sections at this stage the first indication of the for- 

 mation of the mouth is the disappearance of the mesogloea from a small area at the poste- 

 rior end, so that there is no longer a distinct boundary there between the ectoderm and 

 endoderm (m, Fig. 40) . At the same time a small dent appears in the outer surface. 

 This deepens until it forms a minute tube connecting the endodermal cavity with the 

 exterior (Fig. 41) . The mouth thus formed gradually widens and becomes slightly 

 funnel-shaped. 



Further stages in the development of the mouth are represented in Figs. 5, 6, 7. In 

 In Fig. 6 there is a distinct circular groove which outlines the base of the proboscis and 

 separates it from a rudimentary peristome. In Fig. 7 the peristome is well developed, 

 and the mouth is widely open. 



There is no invagination of the ectoderm connected with the formation of the mouth, 

 and there is no oesophagus, " Schlundpforte " or " Taschenvorhang." So, if Goette's 

 account of the formation of the mouth in the sexually produced scyphistomas be accepted, 

 we have here a case where an agamogenetic differs to a marked degree from the 

 gamogenetic course of development. 



The Scyphistoma. With the elongation of the forward end, the formation of ten- 

 tacles, and the development of four gastric pouches, the free-swimming larva becomes a 

 typical scyphistoma. 



By the end of the third or fourth day after the bud has been set free, the forward 

 end of the larva has elongated to form a stem equal in length to the rest of the body 

 (Figs. 7, 8,, 9, and 11) . The end of the stem becomes expanded, generally flattened, and 

 the epithelium covering it becomes deeper than the rest (Fig. 42) . This epithelium pro- 

 duces a secretion which serves to fasten the larva to some solid object. Fixation usually 

 takes place during the fourth or fifth day, but the time varies greatly. 



