772 PROCEEDINGS OF THE ACADEMY OF [DeC. , 



coelenteron has completely divided into two, aud the endodermal 

 wall of the pouch has grown in as a solid partition between the two 

 new pouches. The aboral portion of the body, or hydrocaulus, is 

 seen to be considerably longer than is usually the case. It is 

 interesting to compare, in this connection. Dr. Murbach's account^^ 

 of the transverse fission of Hijpolytus. 



Transformation of the Polyp. 



Up to the present time all efforts to secure specimens of the 

 larval Gonionema in their natural habitat have been well-nigh 

 fruitless. Although the eggs are laid in enormous numbers during 

 four to six weeks of the summer, and even when kept in the 

 laboratory a large proportion develop, it has yet been impossible to 

 find the polyps in the eel-pond where the medusoe are so plentiful. 

 Many speculations have been hazarded as to the condition in which 

 the larvse pass the cold months of winter, and no small energy and 

 time have been expended in attempting to get at the secret. And 

 yet I am much more ready to believe that the difficulty has been 

 with our methods of search than that any extraordinary trans- 

 formation in form or change in habitat should render the success of 

 such search impossible. This seems the more likely from the fact 

 that during the summer when the medusoe are laying their eggs 

 most plentifully, aud within a few days after an egg is laid it has 

 developed into a fixed polyp with tentacles, the extreme minute- 

 ness of size and transparency of substance of the polyps hide Ihem 

 completely ; and yet they must be present in great numbers on the 

 stones and in the mud at the bottom of the eel-pond. Very few 

 specimens have been found, although careful search has been made 

 by others than myself. It is quite out of the question to suppose 

 that the larvse which develop into the medusae appearing each 

 year in great numbers in the eel-pond, have undergone their trans- 

 formation in deep water, having been swept out to sea from their 

 birthplace. In such case the adults would appear in nmch wider 

 range of habitat — in some of the bays and inlets of the coast where 

 the conditions seem almost the same as in the eel-pond. The fact 

 is that only a few stragglers are ever found in the vicinity, not 



"L. MuRBACH, Hydroids from Wood's Hole," Quarterly Journal, Vol. 

 XLII, Pt. 3. 



