Noss. 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 speciali- 
zation which is very similar to what Metschnikoff has described 
in Cunina and has termed sforogenesis.’’ 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. 
