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Cincinnati Society of Natural History. 



ocean, but perhaps attain their maximum development between 500 and 

 1,000 fathoms. They differ very much in habit of growth, for whilst some 

 can only be obtained by dredging at considerable depths, others live near 

 the surface, and others again attach themselves to the surface of rocks and 

 shells between the tide marks. 



The branched sponges, with a compact, feltred tissue, are more common 

 than others in the colder, martime domains, where the species of a loose 

 texture, which grow in large massive forms, either do not exist or are very 

 rare. Many sponges are of considerable size, such as the vase-like tropical 

 species, known under the name of Neptune's Cup. Others are almost mi- 

 croscopical and while by far the greater number grow superficially from a 

 solid base, some penetrate like destructive parasites into the texture of 

 other animals. 



Zoologists generally class the sponge with the protozoa, but Haeckel's 

 investigations led him to decide that the sponge is not a protozoan, but 

 belongs to a type only less highly organized than the lower polyps, and 

 with more analogy to the radiates than the protozoa. He regards them as 

 closely allied to the hydroid polyps, and his reasons are based on the fact 

 that the sponges are made up of two layers of cells (Ectoderm and Endo- 

 derm, or outer and inner layers) surrounding a central cavity, and that 

 both reproduce by eggs and spermatozoa. Gregenbaur and some English 

 naturalists have indorsed this view. 



Lieberkiihn made the discovery — confirmed by Haeckel —that sponges 

 are really Hermaphrodite Animals, reproducing by eggs and sperm cells 

 developed in the same individual sponge. Haeckel showed that they were 

 probably developed from the inner (Endodermal) layer of cells forming 

 the body. These cells transform into an egg in the following manner : at 

 first, provided with a collar and flagellum, it begins to draw these in until 

 they disappear, then a nucleus appears within the nucleolus of the cell. 

 The egg soon becomes detached from the body-wall, and moves about, 

 sometimes penetrating into tfce exoderm or emigrating from the stomach 

 to be fecundated abroad. After fecundation of the egg it begins to 

 undergo self-division, splitting into two, four, eight, sixteen, etc., nucleo- 

 linated cells; the process being exactly as in the eggs of nearly all the 

 higher animals, including man. This stage of segmentation Haeckel 

 terms the Morula Stage. The cells of the Morula afterward separate 

 into two kinds, a few remaining round, the majority becoming long and 

 prismatic, and provided each with a cilium, by means of which it swims 

 about and looks like a "planula" or larval Jelly Fish. This stage 

 Haeckel consequently calls the Planula Stage; the next step is the forma- 



