794 SUMMARY OF CURRENT RESEARCHES RELATING TO 



In the classification of the Hydroid Polyps the absence or presence 

 of the teeniolae gives us I. Intceniolatce with the families Mydrina, 

 Campanularince, and Sertularince, and II. Tceniolatce, divisible into the 

 AcolloblastcB (with fourteen families), where the supporting lamella 

 takes no part in the formation of the tseniolas, and the Colloblaslce 

 (with the families Spongicolidce and Scyphostomidce) where the support- 

 ing lamella enters into the tseniolse. 



A study of the histiogenesis of the Hydroid Polyps shows that any 

 histological element, whether of the ectoderm or of the endoderm, is 

 capable of becoming converted into a generative, muscular, glandular, 

 or other cell ; the part of the endoderm which lines the hypo- 

 stome is regarded as having a secretory function, while that found in 

 the gastric cavity is thought to be digestive. It is important to note 

 that the author has convinced himself that ovarian or sperm-cells 

 are sometimes derived from the ectoderm and sometimes from the 

 endoderm, in face of the definite statements made by some authorities. 



Hydra.*— 0. F. Jickeli, having been attracted by the view of 

 Brandt that Hydra grisea is but a young stage of H". viridis in 

 which the symbiotic Zoochlorella has not yet appeared, has addressed 

 himself to the study of the differences between these species. He 

 finds characteristic marks in the form of the urticating capsules, 

 sufficiently striking to enable one to distinguish, from a small piece 

 of well-preserved ectoderm, from which form the piece was taken. 

 Further than this, H. grisea has in its endodermal cells bodies of 

 a yellowish colour, which take the place of the green bodies of 

 H. viridis, and, as these do not seem to have been detected by Brandt, 

 the author believes that that naturalist had under observation not 

 H. grisea but H. vulgaris {fused), and this view is confirmed by the 

 fact that while H. vulgaris may, in some stations, be quite common 

 in spring, it is very rare in summer when H. viridis is abundant. 



Vital Phenomena of Actiniae.f — B. Solger finds that the Actiniae 

 have no free enzymotic digestive secretion ; treatment of the mesen- 

 terial filaments with water dissolves out a tryptic enzyma in Sagartia 

 and Anihea and a peptic one in Gerianihus ; the yellow bodies (or 

 zooxanthellge of Brandt) which are found in the cells of the 

 endoderm are probably, the author thinks, foreign algae. Neither 

 the cells of the mesoderm nor of the ectoderm are capable of digesting 

 albuminoid bodies ; when a so-called anal pore is present (as in 

 Cerianthus) it does not serve for the evacuation of the faacal 

 masses, but for that of the generative products and the expulsion of 

 water. As to their respiratory phenomena, we find that Actiniae 

 reduce oxyhaemoglobin, but, on the other hand, there are great differ- 

 ences exhibited by them in their power of resisting oxygen-starvation, 

 Sagartia troglodytes living for a long time, S. parasitica dying soon. 

 Some concluding observations are made on the results of recent 

 researches into the chemical constitution of these coelenterates. 



* Zool. Anzeis., v. (1882) pp. 491-3. 



t Biol. Centrall.l., ii. (1882) pp. 399-404. 



