METAZOA COELENTERA. 99 



above; fig. 7, the same in profile; fig. 8 is the beginning 

 of the fourth furrowing stage ; fig. 9, the same a half hour 

 afterward ; fig. 10, the same three quarters of an hour after 

 fig. 8. The rotating movements of the embryo begin at 

 this time. Figs, n and 12 are further developed stages; 

 fig. 13 is the morula stage; fig. 14, the larva with two 

 layers; figs. 15 and 16 are the free-swimming larvae; 

 fig. 17 is the larva with nettle capsule ; fig. 18, a further 

 developed larva; fig. 19, a larva with projecting tentacles ; 

 fig. 20, larva with gastro-vascular cavity; fig. 21 shows 

 the beginnings of the wider tentacles; fig. 22 is a larva 

 forty-five hours old, and fig. 23, one fifty-two hours old ; 

 fig. 24 is a larva with eight tentacles, and fig. 25, one 

 with twelve tentacles; fig. 26 is the same in profile, and 

 fig. 27, the disc of same from above. Fig. 28 is the adult 

 Aglaura. 



In some of the most specialized genera of the Tracho- 

 medusae there are various secondary modifications, and 

 the adult characteristic of a peculiar bell-shaped body 

 appears in the young. 



HYDROPHORA. ANTHOMEDUSAE. 



Acaulis (PL 117, figs. 1-3) may be one of the primi- 

 tive forms of the Anthomedusae, although as yet it is not 

 positively known that the medusae become free. Fig. 



1 represents a portion of a young Acaulis. The blunt 

 posterior end is shown with both the temporary tentacles, 

 which are short and swollen at their ends, and the perma- 

 nent ones which are long and slender throughout. Figs. 



2 and 3 probably represent the adult, one much enlarged, 

 the other natural size. The mouth is at the smaller end 

 with numerous papillae about it ; the temporary tentacles 

 of the young have disappeared. Below the papillae are 

 the clusters of gonophores which Stimpson observed "in 

 an advanced stage of development, soon to become free- 



