No. 6.] AMERICAN MORPHOLOGICAL SOCIETY. 343 



explanation for the reason of their formation. My comparative- 

 studies on the spermatogenesis of a considerable number of 

 species of Hemiptcra, which have brought to light certain facts 

 of importance for determining these questions, render it probable 

 that in the process of formation of the bivalent chromosomes we 

 have a conjugation of paternal with maternal chromosomes. This 

 would then be the final stage in the fertilization of the germ cells ; 

 it would be a conjugation of the chromosomes of different parent- 

 age producing a rejuvenation of them as metabolic centers of 

 the cell ; and this rejuvenation finds its expression in the great 

 changes of the growth period. Then, probably, the reduction 

 division takes place, in order to separate again the conjugating 

 chromosomes, as two conjugating Infusoria unite and then sep- 

 arate after the accomplishment of the rejuvenescence. 



In the space of a short abstract it is not possible to give the 

 evidence for these conclusions. 



XIII. A STUDY OF THE PHENOMENA OF 



FERTILIZATION AND CLEAVAGE 



IN ETHERIZED EGGS. 



EDMUND K. WILSON. 



A. 



IF fertilized eggs of Toxopnenstcs, after the formation of 

 the cleavage-figure, be placed in a 2.^/0 solution of ether in 

 SGSL water, the astral rays quickly fade out, as was long since 

 observed by O. and R. Hertwig in sea-urchin eggs treated by 

 solutions of chloral hydrate or sulphate of quinine. The clear 

 hyaloplasm masses forming the astral centers are thus left as 

 well-defined, slightly irregular, non-radiate areas, connected by 

 the spindle-area. If the eggs are replaced in sea water, the 

 rays are rapidly redeveloped and cleavage may proceed nearly 

 or quite normally. Even if left in the ether solution, how- 

 ever, the nuclear division may be completed, the daughter- 

 nuclei being re-formed and growing to their normal size, but 

 no cytoplasmic division oc curs, - - a result similar to the earlier 



