Eugene Howard Harper 19 



maturation divisions. The body of active protoplasm is differently 

 oriented in the two cases, as has been pointed out. During maturation 

 the active protoplasm underlies the spindle and extends radially in the 

 egg, widening centripetally, so that its appearance is roughly that of a 

 cone from the apex of which the polar bodies are pinched off. At cleav- 

 age, the area assumes a horizontal position with reference to the surface, 

 and a constriction occurs at its middle. At the first maturation division 

 (Fig. 6a), the spindle lies at the center of a granular area encircled by 

 a hyaline zone. From analogy with the cleavage divisions, it would ap- 

 pear that this hyaline zone is a normal cytoplasmic feature of the 

 maturation division. Within it lie many sperm nuclei and it is the 

 favorable zone of eatrance for the male elements. It would thus appear 

 to have a double function, the relations of which are not, however, neces- 

 sarily close, since the entrance of spermatozoa is not confined to this 

 zone. In the second maturation division the hyaline zone around the 

 spindle seems less conspicuous than at the first. 



Kupffer, 75 and go, pointed out that the primary differentiation of 

 protoplasm seen in'tjie unicellular organism, into an outer hyaline and an 

 inner granular protoplasm surrounding the nucleus, is also found in the 

 animal tissue cell and egg. In the egg of petromyzon, as shown by 

 Bohm, to which- Kupffer, go, made especial reference, this differentiation is 

 clearly shown. The hyaloplasm, which during fecundation appears as a 

 cap upon the egg, Mer moves back into the yolk and undergoes further 

 amoeboid changes, elongating in the direction of nuclear division. The 

 behavior of the sphere substance in the egg of unio, as described by 

 Lillie, 01, may be compared with that of the active protoplasm in the 

 pigeon. The sphere substance results from the growth of the egg centro- 

 some- and sphere, and extends across nearly the whole diameter of the 

 egg, elongating in the plane of nuclear division. In the pigeon's- egg one 

 stage was found, of the partially reconstructed egg nucleus, where the 

 centrosome and sphere appeared greatly enlarged, as described by Lillie 

 (Fig. 36). Conklin's demonstration of protoplasmic currents in the egg 

 of crepidula may be mentioned in this connection. As mentioned above 

 Balfour states that in the selachian egg amoeboid movements occur 

 before cleavage begins. Whitman, 87, insisted that the cytoplasm could not 

 be regarded merely as a passive nutritive substance, although, as he said, 

 the majority of writers are inclined to seek the primum mobile in the 

 nucleus and to make the nucleus responsible for the kinetic phenomena 

 displayed in the cytoplasm." 



Loeb, gs, relying upon Quincke's experiments and certain experiments 

 of his own upon the echinoderm egg, ascribes cell-division to diffusion 



