438 BULLETIN OF THE 



two forms of nucleus ; on the contrary, this connection is supported by 

 the following facts : — 



1. They both occupy the same position in the yolk. 



2. The clear non-granular area which surrounds the centrally located 

 spindle corresponds very nearly with the size of the germinative vesicle 

 and appears to result from its dissolution. 



3. An enuclear condition of the egg, if properly treated, could never 

 be made out. 



4. The evidences of the dissolution of the germinative vesicle and the 

 formation of a spindle can be arranged in a continuous series. 



"At maturity of the egg," — thus Hertwig summarizes, — "the germi- 

 native vesicle undergoes a series of changes in that its dot breaks up into 

 several pieces, its membrane is dissolved, and the nuclear fluid (Kern- 

 saft) mixes in part with the yolk. These changes are to a certain extent 

 independent of each other, inasmuch as the dot may persist when the 

 membrane is already dissolved, and vice versa. Out of the fragments of 

 the nucleolus and the remnant of the nuclear fluid arises the fibrous spindle- 

 shaped nucleus^ Whether the accessory nucleoli, and whether the whole 

 or only a part of the nucleolus, contribute to this spindle is uncertain. 

 The migration to the periphery of the vitellus may take place in either 

 of the two conditions of the nucleus. 



The further changes which the excluded egg undergoes within the 

 cocoon were traced on another genus, — Nephelis. The spindle lies 

 already at the time of exclusion in a radial position, with one end near 

 the surface. The first changes are as follows : the rods of the middle 

 zone (Kernplatte) elongate ; the homogeneous areas, especially the pe- 

 ripheral, become larger, and the surrounding rays more prominent and 

 extensive ; the peripheral area is visible in the living egg. Passing over 

 so much as relates to what may be seen on the living egg of the for- 

 mation of the first polar globules, I will enumerate only the internal 

 changes. With the formation of a protuberance of the protoplasm at 

 the animal pole the spindle moves farther and farther from the centre 

 of the egg, for its peripheral tip remains as if attached to the summit of 

 the elevation. The middle zone of thickenings splits into halves, which 

 migrate as in nuclear division generally. The granules remain united 

 by nuclear filaments. In consequence of this, the spindle has increased 

 considerably in length. ^ It therefore comes to lie, when the pinching 



* It seems to me that the lengthening of the spindle is very inconsiderable till 

 near the close of the constriction which forms the polar globule, so that it is not quite 

 exact for Hertwig to refer the lengthening of the spindle to any of the precedmg 



