1902.] NATURAL SCIENCES OF PHILADELPHIA. 759 



the larvse and adult medusae, I find meulhol crystals the most con- 

 venient and rapid chemical to use. 



It may be well to mention the method of keeping Gonionema 

 alive in the laboratory. Running Avater is not desirable, and it is 

 of no benefit to either medusse or larvse to change the water fre- 

 quently, as I have learned after much laborious effort to keep the 

 specimens alive in this manner. Balanced aquaria furnish the best 

 environment for these creatures. I succeeded in keeping a large 

 number of larvse in healthy growing condition for six months in 

 aquarium jars in the laboratory. The quantity of water was kept 

 constant by adding fresh water to make up for the loss by evapora- 

 tion. Food was furnished in the form of protozoans and other 

 microscopic organisms. Oxidation was secured by means of large 

 quantities of diatoms which were reared for the purpose. Cultures 

 were made from the scrapings of eel-grass, etc., and the diatoms 

 which accumulated from them, collecting in clumps on the bottom 

 of the dish, were scraped into the water with the larvse. At the 

 end of January, the polyps, which came from eggs laid ihe pre- 

 ceding August, died Avithout undergoing metamorphosis. Their 

 death was probably due to a lack of food supply sufficient for the 

 requirements of their growing tissues. 



D. Segmentation. — The egg is spherical, averaging .07 mm. in 

 diameter. It consists of yellowish, rather cloudy protoplasm, 

 sufficiently transparent to permit one to observe the more conspicu- 

 ous changes which take place in the substance of the living egg. 



Segmentation is total and equal, of the type which is designated 

 by Melschnikoff as " durschneidende Fu7'chung." The cleavage- 

 furrow appears at one side of the egg first and cuts through its 

 substance until it reaches the opposite side, dividing it into two 

 hemispheres (PI. XXXI, fig. 6). The point at which the furrow 

 starts is that nearest the nucleus, which lies eccentrically in the 

 granular substance of the egg. The first indication of the fiu-row 

 is a shallow groove, which deepens rapidly and at the same time 

 lengthens so as to embrace the egg meridianally. The furrow is 

 finally completed, superficially, a short time before it has entirely 

 separated the egg into two distinct halves. The last point to lie 

 cut off corresponds in position almost exactly with the nucleus, but 

 on the opposite side of the egg. The first cleavage is completed 

 one hour after fertilization. The two dautihter-uuclei now lie at 



