330 KING. [Vol. XVII. 



irregular reticulum (PI. XXXI, Fig. 50) which shows no signs 

 of the thickenings found by Eismond ('94) in the astrospheres 

 of Triton. The radial systems, having reached their greatest 

 extent at the previous stage, are now less pronounced, although 

 they are still distinctly visible. A layer of pigment granules 

 forms around the centrospheres, and also around the male pro- 

 nucleus, which, now that the connection between the centers is 

 broken, occupies a position between them. In the next stage 

 (PI. XXXI, Fig. 51), when the two pronuclei are in contact, 

 every trace of the radial systems has disappeared and the astro- 

 spheres are round masses containing a distinct granular reticu- 

 lum and surrounded by a very thick layer of pigment which is 

 evidently formed of the pigment granules which previously 

 marked the course of the astral rays. 



These later changes are comparable to those described for 

 Axolotl, where, at the time the two pronuclei are about to 

 unite, the radiation around the two centers has entirely disap- 

 peared and the centers themselves appear as compact, round 

 structures showing; no sisrn of a centrosome. 



4. Fusion of the Pronuclei and Formatiofi of the First 

 Segmentation Spindle. 



The male pronucleus grows very rapidly and soon outstrips 

 the female pronucleus, measuring 0.022 mm. in diameter when 

 the latter has a diameter of but 0.018 mm. (PI. XXXI, 

 Fig, 50), In structure both pronuclei appear the same, each 

 being nearly spherical and containing a reticulum seemingly 

 composed of fine linin fibers. A number of rounded nuclear 

 masses, presumably chromatin, lie either at the intersections 

 of the fibers of the reticulum or in the nucleoplasm close to 

 the nuclear membrane. 



The two pronuclei can be readily distinguished until they 

 come in contact and are about to fuse (PI. XXXI, Fig. 51). 

 From the moment of its formation the female pronucleus lies 

 naked in the protoplasm in close contact with the yolk granules. 

 It is never accompanied by an astrosphere or any radiation ; nor 

 is it ever surrounded by a layer of pigment or an accumulation 



