INITIATION OF. DEVELOPMENT IN EGG OF ARBACIA. 



403 



medium. If this be true, it would perhaps account for the fact 

 that I obtained much higher percentages of cleavage and of plutei 

 from my inseminations than Moore from his. 



Moore, as mentioned above, found scant evidence in his cyto- 

 logical study of any pronounced activity of the sperm. However, 

 I am sure that in my material the sperm is quite active; it may 

 form an aster, swell, and form chromosomes. (Cf. Herbst's 

 studies.) 



The method employed in these experiments is simple. Eggs 

 from one Arbacia are collected as free from ccelomic fluid as pos- 

 sible, washed, allowed to settle, and exposed to hypertonic sea- 

 water (in the proportion of 8 parts 2y 2 M NaCl or KC1 to 50 

 parts sea-water). After varying lengths of time eggs are re- 

 moved to normal sea-water. When they have reached the desired 

 stage monaster, metaphase, etc. a portion is lightly inseminated 

 with fresh, clean sperm suspension. The development of the in- 

 seminated eggs is compared with that of the uninseminated per 

 cent, of membranes, cleavage, and swimming larvae. The follow- 

 ing table presents the essential results of some of these experi- 



TABLE I. 



COMPARISON OF THE EFFECT OF EXPOSING EGGS OF Arbacia TO HYPERTONIC 



SEA-WATER (IN THE PROPORTION OF 8 PARTS 2^/2 M NAL * TO 50 



PARTS SEA-WATER) ALONE WITH THAT OF INSEMINATING EGGS 



IN WHICH NUCLEAR CHANGES HAVE BEEN* INDUCED BY 



HYPERTOXIC SEA-WATER. 



* KG gives similar results. 



