smallwood: maturation of h amine a solitaria. 301 



elongated and slightly constricted (cf. Limax agrestis, Byrnes, '99, p. 213, 

 PI. xi. Fig. -i). It still lies near the periphery of the egg, though the 

 second maturation spindle has been formed. On the other hand, the 

 sperm head represented in Figure 63 lies somewhat deeper in the egg 

 than in the case of Figure 61, is swollen and nearly spherical, and 

 already contains a single vacuole of irregular form and ill-defined out- 

 line, although the egg is only in the anaphase of the first maturation. 

 These two cases illustrate sufficiently the lack of correlation between the 

 development of the sperm head and the maturation of the egg. A con- 

 siderably more advanced stage in the metamorphosis of the sperm head 

 is seen in Figure 84 (Plate 12). The head has now assumed the ap- 

 pearance of a vesicular nucleus, and has moved into the region near the 

 animal pole which is destitute of deutoplasm ; it has a thick, deeply 

 staining wall, and is considerably larger than in the stage last mentioned ; 

 it contains, in addition to linin threads and chromatin, a homogeneous 

 ground substance which stains very faintly. Further changes in the male 

 pronucleus are represented in Figures 53 (Plate 8) and 85 (Plate 12). 

 The wall is no longer thick, but it still takes a light stain, and may 

 become irregular in outline ; the linin fibres have united to form a scanty, 

 coarse-meshed network, on which are located the chromatin masses. 

 In one instance the male pi'onucleus had already assumed a condition 

 similar to that of the female pronucleus shown in Figure 51 (Plate 8), 

 wliile the second maturation figure was only in the telophase. 



From the time that the spermatozoon enters the egg until the ana- 

 phase of second maturation, there is no evidence of an aster in the egg 

 aside from those associated with maturation. The progress of the sper- 

 matozoon through the deutoplasm is unattended by any evidence of 

 radiation. In three instances, during the late anaphase of the second 

 maturation, an aster (not figured) has been found in the centre, or very 

 near the centre, of the egg. In no case could any connection be made 

 out between these asters and the sperm head. 



4. Early Cleavage. 



(a) Metamorphosis of the Chromatin. 



Since there seem to be no essential differences in the process of meta- 

 morphosis in the female and male pronuclei, the earlier changes in the 

 sperm liead (p. 300) excepted, I shall confine my description to the 

 female prunucleus. 



The first difi"erentiation of chromatin is observed when the vesicles, 



