ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



793 



Organization of Hydroid Polyps.* — Dr. O. Hamann finds that in 

 Hydroid Polyps there is rarely more than one — the longitudinal — axis ; 

 sometimes, however, the tentacles may be seen to be arranged along 

 definite rays, so that the symmetrical arrangement of organs is not 

 confined to the Medusae ; he shows that other genera besides Tubularia 

 are provided with taeniolae, and he uses the presence or absence of 

 this character as an important aid to classification. In the Taeniolatse 

 he finds an endodermal musculature not only in the hypostome, to 

 ■which it is confined in the Intaeniolatas, but also in the stomach. 



True sensory cells or nerves were never detected in the ectoderm, 

 and the structures which seemed to be such were found on closer 

 examination to be merely interstitial cells. The endoderm of Aglao- 

 phenia was found to be filled with yellow cells, which appeared to be 

 unicellular algae taken in for the purposes of nutrition. The cells of 

 the ectoderm were found to be (1) epithelio-muscular cells, (2) 

 proper epithelial cells, (3) interstitial, deeper-lying cells, (4) true 

 muscle cells, (5) interstitial cells converted into cnido-cells, and (6) 

 glandular cells ; after describing these the author passes to the 

 supporting lamella, which is nothing more than a structureless thin 

 sheet, which is secreted from the endoderm. 



In dealing with the origin of the Medusae, Dr. Hamann starts from 

 a polyp-stock, any cells of which might become an egg-cell or a sperm- 

 cell ; imagining that separate persons might become broken off or 

 separated from the colony, we can suppose that if they become adapted 

 to the new conditions they would continue to reproduce their kind, 

 but they would at the same time be modified by their new life, become, 

 in fact, Medusce ; it will be seen that the complete homology of the 

 Polyp and Medusa is here recognized. The planula is stated to be 

 always formed by delamination or by the wandering of ectodermal 

 cells. 



The relations of various Ccelenterata are exhibited in the following 

 table :— 



Siphonophora 



Koralla 



Scyphostoma 



Spongicolidae 



TiENi'oLAT.E Int^niolat^; Htdrocoralline^e 



Hydra (1) Sertularinae 



(2) Campanulariuae 



(Hydrusae) 

 Archydra. 



* Jcnaisch. Ztifcehr. f. Xaturwiss., xv. (1882) pp. 473-544 (6 pie.). 



