THE GONOPHORES OF THE HYDROCORALLIN^. 201 



Hydroiden ist wohl Hydra ; es scheint mir wenigstens fur 

 jetzt kein Grund vorzuliegen, sie fur eine riickgebildete Form, 

 wohl aber manche Griinde sie fur eine sehr alte Form zu 

 halten, wie oben schon genauer begriindet wurde, und wie es 

 audi so von den meistea Forschern angenommen wird " (12). 



Both of these authors considered that the primitive type of 

 Hydrozoan was a simple sessile form more or less similar to 

 our modern Hydra, and that the medusa originated by the 

 modification of individuals bearing the sexual cells that were 

 budded from, and set free from, the primitive simple sessile 

 Hydra. 



Lankester says, " The particular form which the proximate 

 ancestor of the Hydrozoa took is most nearly exhibited at 

 the present day in Lucernaria, and in the scyphistoma larva 

 (Hydra tuba) of Discomedusae. It was a hemispherical cup- 

 like polype with tentacles in multiples of four, with four lobes 

 to the wide enteric chamber. This polype, after passing a 

 portion of its life fixed by the aboral pole, loosened itself and 

 swam freely by the contractions of the circular muscular fibres 

 of the hypostome (sub-umbrella), and developed its ovaria and 

 spermaria on the inner walls of the enteric chamber. This 

 ancestor possessed, like its descendants, a very marked power 

 of multiplication, either by buds or by detached fragments of 

 its body. Accordingly it acquired definitely the character of 

 multiplying by bud formation during the earlier period of its 

 life ; each of the buds so formed completed in the course of 

 time its growth into a free-swimming person. We must sup- 

 pose that the peculiarities of the two phases of development 

 became more and more distinctly developed, the earlier budding 

 phase exhibiting a more elongated form and simple enteric 

 cavity (Hydra form), which subsequently became changed in 

 the course of ontogeny into the umbrella or disc-like form, with 

 the coalesced enteric walls and radial and circular surviving 

 spaces (medusa form). And now the ancestry took two distinct 

 lines, which have given rise respectively to the two great groups 

 into which the Hydrozoa are divided — the Scyphomeduste and 

 the Hydromedusse." 



