MUSEUM OF COMPARATIVE ZOOLOGY. 299 



line nucleus is, in Goette's opinion, certainly the initiatory point of the 

 whole development. Subsequently its outline melts away, and with it 

 the significance of the nucleus itself; the "life-germ," however, remains, 

 and surrounding it — though not sharply marked off from it — an area 

 of fine-granular yolk substance, which is not constant in size, nor in the 

 sharpness of its limitation from the remaining yolk (pp. 54, 55). 



Soon after its formation the life-germ is elongated in a direction 

 transverse to the axis of the egg. Its ends enlarge at the expense of 

 the middle portion, which continues to grow more slender as the ends 

 diverge from each other. It at length breaks, and the halves become 

 rounded, having meantime begun to increase, so that eventually each 

 attains the size of the first " life-germ." As observed in subsequent life- 

 germs, the elongation results from a change in the foj*m of the germ, 

 whose remaining axes shorten, and is not, therefore, due simply to a 

 growth at two opposite points (pp. 55, 60). From what is said of the 

 division of the Jirst life-germ (p. 55), one would infer that the changes of 

 the surrounding " area " followed those of the germ ; but it is distinctly 

 stated in another place (p. 61) that this finely granular substance of the 

 area initiates the motion in two opposite directions, itself dividing into 

 two masses before the germ does. 



After the second division of the yolk, there is an essential change in 

 the contents of each life-germ ; namely, a variable number of round, 

 clear corpuscles appear in the apparently homogeneous germ-substance, 

 which are the "nuclear germs" (Kernkeime). These are so soft that 

 they become elongate at the subsequent division of the life-germ. 

 While the Kernkeime augment and thereby consume the substance of 

 the latter, it, together with its surrounding " area," melts into a single 

 delicately granular mass, in the middle of which the compacted Kern- 

 keime fill up the space which the original life-germ had occupied. 



As the nuclear germs supersede the life-germ spatially, so they do 

 functionally in the subsequent divisions of the yolk. During the mul- 

 berry stage the division occurs so rapidly that the nuclear germs have 

 not time to attain the centre of the finely granular mass before the lat- 

 ter has begun to elongate preparatory to the next division, which is 

 usually effected along a plane perpendicular to that of the last preced- 

 ing. At the close of the division the fine-granular mass appears radi- 

 ally streaked about the nuclear germ [aster], and likewise delicate dark 

 lines converge from the plane of division toward each of the germ masses 

 [spindle]. New nuclear germs constantly arise, not so much by division 

 as probably out of the amorphous fine-granular mass, and associate 

 themselves with those already formed. 



