SCHULZe's memoir on COKDYLOPHOaA LACUSTRIS. 39 



looked it, were it not that its presence in this place is incon- 

 sistent with what seems to be the true origin of the generative 

 elements. 



With regard to the origin of the generative elements, 

 Schvilze views them as ectodermal products. In this I 

 cannot agree with him. I believe I have satisfactory evidence 

 of their endodermal origin in several marine hydroids. There 

 can be no doubt that in these the generative elements, which 

 in all cases lie between the ectoderm and endoderm of the 

 gonophore, become more and more mature as they recede from 

 the endoderm which confines them internally, a fact which is 

 scarcely compatible with any other view than that they are 

 products of the endoderm with which the young portions of 

 the mass are still in connection rather than of the ectoderm. 



It is true that if the " stiltzlamelle" as Schulze supposes, 

 can be proved to invest the spadix at this period, and to form 

 a continuous and unbroken layer between it and the ova or 

 spermatozoa, a strong argument for the ectodermal origin of 

 the generative elements would be afforded, but, with the very 

 decided evidence we possess of their origin from the endoderm, 

 I must suspend my belief in the validity of this observation.^ 



The author has followed the development of the embryo 

 through its planula stage. In this stage he believes he 

 has detected the foundation of the " stiltzlamelle" between 

 endoderm and ectoderm, though unable to isolate it as an 

 independent membrane. He could as yet detect no cilia on 

 the endodermal cells, whose free ends seem to be as in those 

 of the fully developed hydroid deprived of membrane. He 

 admits that in the young tentacles of the developing hydroid 

 the endoderm which clothes the internal cavity of the body 

 is continued into the solid core of cells which forms their 

 axis, and he follows KoUiker in regarding this as a proof 

 that true epithelial cells may be transformed into a tissue 

 which just as undoubtedly belongs to the connective sub- 

 stances as the tissue of the Clwrda dorsalis or of cell-car- 

 tilage. 



With regard to the mode of life of Cordylophora laciistris — 

 the only species which he recognises — he believes this hydroid 

 to be truly a brackish-water animal. There can be no doubt 



' Indeed, I now believe that the very delicate, clear, structureless mem- 

 brane which I iiave elsewhere described as beiusf in many cases carried our, 

 hernia-like before the ova when these are expelled under pressure from the 

 gonophore, is uothintc more than this " stiitzlamelle." If so, the ova must, 

 have been produced between the latter and the spadix. I believe too that I 

 have in some instances, as in Laomedea calieulata, a hydroid with a branch- 

 ing spadix, detected a delicate structureless membrane ^aw///^ over the ova 

 while these are still in contact with the spadix. 



