No. 3- DEVELOPMENT OF MARINE SPONGES. 373 



is the remarkable development of the hydromedusa, Epenthesis 

 McCradyi, described by Brooks (39). The novel development 

 of this jelly-fish is thus sketched in the opening paragraph of 

 Professor Brooks's paper : "In June, 1889, I found at Nassau, 

 N. P., in the Bahama Islands, a few specimens of a hydro- 

 medusa belonging to the family Eucopidae (Haeckel), bearing 

 upon each one of its four reproductive organs a number of 

 hydroid blastostyles from which young medusae are produced 

 by budding ; a method of reproduction which has no exact 

 parallel among the hydroids nor, as far as I am aware, any- 

 where else in the animal kingdom ; for the reproduction, by a 

 medusa, of blastostyles which are morphologically equivalent 

 to hydras, is a reversion, through asexual reproduction, to a 

 past larval stage; a phenomenon which is thoroughly anomalous 

 and exceptional." 



While Brooks regards the production of blastostyles on the 

 medusa as a case of asexual reproduction, he finds they are not 

 produced as simple buds. The ectoderm of the blastostyle is 

 continuous with the ectoderm of the medusa, and arises as a 

 bud-like outgrowth from the latter. The endoderm of the 

 blastostyle has, however, no connection with the endoderm of 

 the medusa, but is rooted in the mass of germ cells composing 

 the reproductive organ of the latter. " These germ cells give 

 rise to the endoderm of the blastostyle by a process of sjDeciali- 

 zation which is very similar to what Metschnikoff has described 

 in Cunina and has termed sporogcnesis." The formation of 

 blastostyles in Epenthesis is thus a composite method of 

 reproduction, a part of the blastostyle being formed by bud- 

 ding, and a part by the development of rudimentary germ 

 cells. Professor Brooks's opinion of this interesting develop- 

 ment had best be given in his own words : " It is probable 

 that Epenthesis is also an example of sporogenesis, and that 

 the endodermal tube is derived from a single cell by segmen- 

 tation, but this is certainly not true of the ectoderm of the 

 blastostyle, and if we have sporogenesis at all in Epenthesis, 

 we have it in combination with budding." 



At the root of Weismann's theory of inheritance lies the 

 supposed essential difference between somatic and germ cells. 



