IV 



COELENTEKATA 



B 



59 



yenec* 



FIG. 35. Four transverse sections through the developing gonophore of 

 Tubularia mesembryanthemum. (After Gotte.) 



A, section through base of gonophore showing the four 

 taeniolae ; t, taeniola. B, section through upper part of older 

 gonophore ; r.c, radial canal ; r'c', spot where two radial canals 

 .join ; sp, spadix ; u, spaces, portions of the irregular umbrella- 

 cavity. C, section through still older gonophore; letters as 

 before ; en. I, so-called endoderm lamella. D, section through 

 almost mature gonophore. r.c, remnants of cavity of radial 

 canals ; gen.ect, generative ectoderm clothing the spadix. 



gen 



FIG. 36. Longitudinal section 

 through very young gono- 

 phore-bud of Tubularia mes- 

 embryanthemum to show the 

 origin of the genital cells. 

 (After Brauer.) 

 Letters as in Fig. 34. In addi- 

 tion : gen 1 , genital cells originating 

 in ectoderm ; geift, genital cells which 

 have penetrated into endoderm. 



When we contrast with this develop- 

 ment the life-history of the free medusae 

 so far as it is known, we find many marked 

 differences. Our principal source of in- 

 formation on this subject is Metschnikoff 

 (1886), who captured the free medusae of 

 Tiara, Rathkea, Oceania, Clytia, etc., and 

 kept them in aquaria till they had de- 

 posited their eggs. He was then able to 

 rear the embryos through the larval stages, 

 until they produced young hydroid colonies. 



In nearly every case he found that the 

 egg underwent a very regular segmentation 

 which led to the formation of a blastula ; 

 this was at first spherical but soon became 



