630 TRANSACTIONS OF SECTION D. 



2. A Gytological Study of Artificial Parthenogenesis in Strongylocentrotus 

 purpuratus. By Edward Hindle, Ph.D., A.R.C.S. 



This investigation was undertaken mainly with the object of tracing the 

 cytological changes that follow the chemical fertilisation of sea-urchin eggs by 

 means of a monobasic fatty acid, followed by treatment with hypertonic salt 

 solution. 



The experimental part of the work was performed, under the direction of 

 Professor Loeb, at Pacific Grove during the month of January 1910. The eggs of 

 S. purpuratus were obtained by removing the gonads from a female and allowing 

 them to remain in a dish of sterilised sea-water for a few hours, when the ripe 

 eggs drop out of the ovaries and fall to the bottom of the dish. 



Membrane formation was effected by putting the eggs in a mixture of 50 c.c. 



N 

 sea-water + 2'9 c.c. of - butyric acid for from 90 to 150 seconds. On trans- 

 ferring them from this mixture to normal sea-water the eggs then formed ferti- 

 lisation membranes. Some of these eggs were allowed to develop without further 

 treatment, but at ordinary temperatures (15° C.) very few of them completed even 

 the first division. 



When the eggs from the butyric-acid solution had remained hi normal sea- 

 water for about 20 minutes they were then placed into a mixture of 50 c.c. sea- 

 water + 8 c.c. of 2g N — NaCl, and exposed to the action of this solution for 

 times varying from 30 to 60 minutes. Finally, the eggs were again transferred 

 to normal sea- water; and if the periods of exposure had been correctly chosen, 

 practically all of them developed and gave rise to free swimming larvae, indis- 

 tinguishable in form and behaviour from those that develop from normally 

 fertilised eggs. 



The developing eggs were fixed at various stages, imbedded in paraffin, 

 sectioned and stained in the usual way. 



A. After treatment of the eggs of Strongylocentrotus purpuratus with 

 butyric arid alone the following changes were observed: — ■ 



1. The first change is the starting of a process of cytolysis as a result of the 

 solution or liquefaction of the ectoplasmic layer immediately within the outer 

 membrane of the egg. As a result of this cytolysis the surface membrane 

 becomes lifted away from the protoplasm of the egg and appears distinct. 



That the formation of this fertilisation membrane is due to a process of 

 cytolysis is proved by the fact that almost any cytolytic agent is able to produce 

 if (acids, alkalies, digitalin, solanin, saponin, fat solvents, alcohol, distilled water, 

 blood-serum, &c). 



2. The membrane-formation is accompanied by an alteration in the appear- 

 ance of the nucleolus, which, from being a densely staining mass of chromatic 

 substance, changes to a lightly staining body of somewhat indefinite shape, or 

 may even break down into two or more lesser bodies. 



3. A dissolution of the cytoplasmic granules in the immediate neighbourhood 

 of the nucleus results in the appearance of a clear perinuclear zone. Probably as 

 a result of currents ilowing centripetally from the cytoplasm towards the nucleus, 

 radiations appear in and around this zone. 



1. The appearance of this perinuclear zone is succeeded by a period of nuclear 

 growth. 



5. In eggs that arc developing at ordinary temperatures a large monaster is 

 usually developed, its rays centring in the nucleus. The nuclear membrane, dis- 

 appears and the chromatin breaks up into eighteen chromosomes. These may 

 undergo division and be drawn out of the nuclear area along the rays, in which 

 case they appear scattered throughout the cytoplasm. A reduction of the astral 

 rays may be followed by reconstruction of the original nucleus with an increased 

 number of chromosomes, and this process may be repeated two or three times. 

 Such eggs never divide, but simply disintegrate. 



(i. Eggs developing at a low temperature (2° to 5° O.) may complete the first 

 few divisions. 



7. Cytasters have never been observed. 



