200 MORGAN. [Vol. IV. 



protoplasm. There is no sharp line of demarcation in the 

 .section between yolk and surrounding protoplasm, but the 

 latter sends processes into the former. 



Passing to a stage represented by Fig. 14, we have essen- 

 tially the same conditions as in the last figure. The ovum has 

 increased very much in size, and the increase is largely due to 

 the accumulation of yolk. Around the periphery of the ovum 

 is a zone of protoplasm which does not contain yolk, and outside 

 of this is the follicular protoplasm with its nuclei. As a rule, 

 the nucleus of the ovum lies near to the centre of the Qg%, but 

 in the section from which the figure was drawn it was near one 

 end of the q%^. It was also irregular in outline, but this is 

 exceptional at this stage. In Figs. 15 and 16 we have the 

 first indication of an origin of the test-cells. In Fig. 15 only 

 a part of the egg is shown, but it will be easily seen that there 

 has been a very great increase in size as compared with Fig. 

 14. At the periphery of the yolk lies a narrow zone of proto- 

 plasm, and the follicular protoplasm around the Q.gg is wider 

 than in the last figures. Here and there a nucleus lies nearer 

 to the inner part of the zone, and it is generally accompanied 

 by an ingrowth of protoplasm from the follicular zone. These 

 ino^rowths are the first trace of the formation of the test- 

 cells. Where they project into the ovum, they are clearly seen 

 to push through the peripheral zone of protoplasm of the Q^^g. 



The follicular zone stains differently from the protoplasm of 

 the ovum, and one thus distinctly sees that the ingrowth of pro- 

 toplasm with its contained nucleus belongs in each case to the 

 follicular zone and represents migrating cells into the proto- 

 plasm of the egg. In Fig. 16 we see three stages in the in- 

 growth of follicular cells. The earliest is shown at tc, where an 

 ordinary follicular nucleus has moved a little interior to the 

 general row, and at the same place the follicular protoplasm has 

 become thickened on the inner side. At tc^ the follicular nu- 

 cleus has passed still further within, and the surrounding proto- 

 plasm projects further into the egg, passing through the zone 

 of protoplasm. At /r" we see a somewhat exceptional condi- 

 tion, owing to the large amount of follicular protoplasm which 

 has pushed into the ovum. It has passed the zone of proto- 

 plasm of the egg, and projects into the yolk substance. Within 

 it and at its base lies a follicular nucleus. In later stages all of 



