A Cytological Study of Artificial Parthenogenesis etc. 153 



which the protoplasm becomes broken up into a mass of small par- 

 ticles lying within the fertilization membrane. 



If, after treatment with butyric acid, the eggs are kept at a 

 low temperature (2 5 C.) the first few divisions may be accomplished. 

 In this case the period of nuclear growth is succeeded by the almost 

 complete disappearance of the perinuclear zone, and the subsequent 

 development of a typical amphiaster in the region of the nucleus. 

 The succeeding changes are identical with those described below, 

 that take place in eggs that have been subsequently treated with 

 hypertonic solution. 



We have never observed any cytasters to be developed in eggs 

 treated with butyric acid alone; usually a monaster appears which 

 may divide to form a typical cleavage -aster or, more often, re- 

 mains undivided. In all cases, therefore, the rays that develop in 

 these eggs originate from the nucleus and do not have an indepen- 

 dent cytoplasmic origin as in the case of cytasters. 



Internal Changes after Treatment with Butyric Acid 

 followed by a Hypertonic Solution. 



(LOEB'S improved method of artificial fertilization.) 



The interval (about 20 minutes) between the transference of the 

 eggs from butyric acid to normal sea water and their subsequent 

 treatment with hypertonic salt solution is characterized by the 

 alterations in the appearance of the cytoplasm and nucleolus, and 

 the subsequent development of a perinuclear zone, as described above. 

 The nucleus then commences to grow and faint radiation can some 

 times be seen extending from the perinuclear zone into the surround- 

 ing cytoplasm (Fig. 2). 



During immersion in the hypertonic solution there are no apparent 

 changes beyond a slight reduction of the clear zone of hyaloplasm 

 surrounding the nucleus (Fig. 3). 



After the eggs are put back into normal sea water the internal 

 changes resulting in the first cleavage follow each other in quick 

 succession. The first change noticed is an increase in the development 

 of the perinuclear zone, followed by further growth of the nucleus. 

 Meanwhile, the meshwork of chromatin becomes coarser and more 

 aggregated together and the nucleolus gradually disappears. This 

 stage is succeeded by a reduction of the perinuclear zone together 

 with its radiations. 



