18 PROFESSOR ALLMAN. 



other Hydroida ; in these the superficial ciliated cells of the 

 planula almost certainly pass into a permanent constituent of . 

 the body walls, while the chitinous perisarc is not a tissue at 

 all, but a mere hardened excretion from the surface. I regard 

 the perisarc, notwithstanding its persistence, as homologous 

 with the internal germ shell of Hydra; indeed in some species 

 (e. g., Eudendrum ramosum) we find it forming a closed sac 

 in which the whole of the young hydroid continues to be 

 included even after the appearance of the rudimental tentacles 

 exactly as seems to be the case with the inner germ shell of 

 Hydra. 



There is thus a difficulty in applying Kleinenberg's deduc- 

 tions to the marine Hydroida and regarding the superficial 

 cells of these as the representative of a nervo-muscular sys- 

 tem, for we should then be compelled to derive the nervo- 

 muscular system of these hydroids from that part of the outer 

 germ lamella which in the Vertebrata gives origin to the 

 epidermal structures, and thus reduce to a mere non-essential 

 resemblance the parallelism which appears in other respects 

 so Avell established between vertebrate and ccelenterate 

 development. 



When we bear in mind that the embryonic condition which 

 shows itself in the presence and primary relations of the germ- 

 lamella becomes soon lost during the process of development 

 of the higher animals, while the outer and inner germ-la- 

 mellae Avith their relations to one another and to the sur- 

 ' rounding world are retained as ectoderm and endoderm through 

 the life of the Coelenterata we at once see wherein consists 

 the low position of the Coelenterata in the animal kingdom, 

 and can compare the permanent Coelenterate type with au 

 early stage in the development of the higher animals. 



It will be seen from the account now given that the re- 

 searches of Kleinenberg have resulted in some very valuable 

 additions to our knowledge of the structure and life-history 

 of Hydra. In some respects they differ from those made by 

 myself on the same animal; but as my opportunities of inves- 

 tigating Hydra have been comparatively few, while such exa- 

 mination as I was enabled to make were not aided by the 

 very reliable methods adopted by our author, I am not pre- 

 pared, at least in the absence of additional observations under- 

 taken with the view of verification, to defend them, and am 

 willing to accept, not only those points of the memoir which 

 agree with my own conclusions, but most of those also which 

 take a different view. 



