16 G. O. Sårs. 



this reason I have never here met with these spheres on the 

 very surface of the sea. In order to obtain them, it is 

 therefore necessary to let the tow-net down to a certain 

 depth, from 20 to 50 fathoms, and to keep it at this depth, 

 when working, by the aid of a heavy weight attached to 

 the rope. The contents of the tow-net have at once to be 

 put in strong alcohol of 96°/o, which, on the return from 

 the excursion, should be renewed. If it is intended to 

 observe the spheres in a fresh and healthy state, great care 

 should be taken immediately to pour off the contents of the 

 tow-net into large bottles filled with water taken from the 

 same depth. Otherwise the oosphères will in a very short 

 time wholly lose their original character, and begin to undergo 

 decomposition, the surrounding membrane of the enclosed 

 ovum becoming in such cases ruptured, and the contents re- 

 ceived into the hollow of the sphere, where it will form an 

 irregular mass, in which a number of larger globules or 

 lappets of a nearly homogenous structure, and apparently 

 consisting of a fatty matter, are seen, surrounded by a more 

 opaque granular substance. In the spermatospheres also in 

 such cases essential alterations occur, the cortical substance 

 of the spermatocyst becoming ruptured in some place or other, 

 and the central mass partly evacuated into the hollow of 

 the sphere. 



III. 



Cleavage of the ovum. 



The cleavage or process of segmentation of the ovum 

 admits of being rather distinctly observed on examining the 

 oosphères in a fresh state (cf. Pl. 1), and in some cases 

 the segments even appear much more sharply defined, than 



