128 EXTERNAL FACTORS III. 8 



poison that the normal vitelline membrane cannot be formed and 

 consequently many spermatozoa enter. In such eggs segmenta- 

 tion does not occur in the ordinary fashion by successive binary 

 divisions, but many small cells are simultaneously formed. The 

 resulting blastulae are abnormal, the segmentation cavity being 

 filled with a solid granular mass (Stereoblastulae), and very few 

 reach the Pluteus stage. The irregularities of segmentation are 

 due to the complex mitotic figures and divisions which poly- 

 spermy entails. One, two, three or more of the spermatozoa 

 fuse with the female pronucleus ; each has its own aster, which 

 divides into two. Hence the most complex nuclear figures are 

 formed. 



In the case where two sperm-nuclei unite with the egg- 

 nucleus a tetraster is formed, that is four asters united by 

 spindles in a square or rhombus, or a triaster with an odd 

 aster united to one angle of the system. The chromosomes are 

 grouped in the equators of the four, or three, united spindles, as 

 the case may be, and the egg divides simultaneously into four, 

 or three. 



The arrangement becomes still more involved when there are 

 other sperms, whether these fuse with the female pronucleus or 

 not. Each amphiaster is united by one pole to the tri-, tetra-, 

 or polyaster developed round the combination nucleus, or to the 

 poles of other amphiasters; in one case there were nineteen 

 spindles in all, not, of course, all in one plane. Each centro- 

 sphere receives half the chromosomes of the spindle attached 

 to it, and each cell, when division occurs, contains one or more 

 nuclei. 



Hydrochlorate of morphine will produce similar effects, but 

 only with longer exposures a 0-4 % solution for from two to 

 five hours. Strychnine, however, is poisonous in very weak 

 doses (-005 % to 25 %), and quite short exposures are sufficient 

 to call forth marked results. Other solutions successfully tried 

 were chloral hydrate (from 0-2 % to 0-5 % for from one to four 

 and a half hours), cocaine (from 0-025 % to 1 % for five minutes), 

 and sulphate of quinine (-05 % for ten minutes). In quinine 

 (05 % for thirty minutes) and chloral (-5 %) the entrance 

 cone was small and no asters were formed, from which the 



