No. 6.] AMERICA* MORPHOLOGICAL SOCIETY. 345 



inwards and gradually enlarges, becoming finally (1-2 hours) 

 as large as the egg nucleus and indistinguishable from it. In 

 some cases, though this is not very common, the two nuclei 

 approach and finally completely fuse to form a typical cleavage 

 nucleus. If in the earlier stages of the process (before union 

 of the germ nuclei and while the sperm nucleus is still not 

 more than two-thirds the diameter of the egg nucleus) the 

 eggs be replaced in pure sea water, the sperm-aster is rapidly 

 developed, centering in a point at one side of the sperm 

 nucleus, and development may proceed normally ; but this 

 result was never obtained after the germ nuclei had united, 

 probably because the action of the ether had been too pro- 

 longed. In a few cases, after replacing the eggs in sea water, 

 the sperm-aster was observed to divide and form an amphiaster 

 before union of the germ nuclei. In this case the sperm 

 nucleus at the time of union had assumed the vesicular form, 

 though still somewhat smaller than the egg nucleus. One 

 such case was followed out and found to give rise to a normal 

 larva. In such cases the effect of the ether has been to trans- 

 form the type of fertilization from that characteristic of the 

 sea urchins into that observed in starfishes, or in many worms 

 and mollusks, where an amphiaster is formed before union of 

 the germ nuclei and the latter are approximately equal at the 

 time of union. 



The foregoing facts show, in general accordance with the 

 early work of O. and R. Hertwig, that growth of the sperm 

 nucleus and approach and fusion of the germ nuclei may take 

 place quite independently of the sperm-aster ; further, that 

 approach of the nuclei is probably not a simple chemotactic 

 phenomenon, since it is very greatly delayed by etherization of 

 the egg. 



C. 



In some of the etherized eggs, after replacement in sea 

 water, the nucleus failed to divide at the first cleavage, the 

 whole of the chromatin passing to one pole and re-forming 

 as a single nucleus. Such eggs divide into a nucleated and 

 a non-nucleated half, the latter containing only an aster, as in 

 the case of some of the non-nucleated egg fragments fertilized 



