The Germ-cells of Lophius. 581 



separated, while in other cells of the embryos the plasmosome 

 material forms two large masses or a single mass of still greater 

 size. The amount of plasmosome material is very much greater 

 in body cells than in the germ-cells. The plasmosomes of the 

 somatic cells are commonly near the center of the nucleus while 

 those of the germ-cells are nearly always on or near the nuclear 

 membrane (figs. 29-33).^ 



b. Later period. Under this heading are described changes 

 seen to be taking place in stage 14 and to a less extent in stage 13. 

 In stage 14 the gsrm-cells occupy a position on either side of the 

 base of the mesentery. They are much more closely aggregated 

 than in earlier stages, and surrounding them are flattened cells 

 derived from the peritoneum, undoubtedly the beginning of 

 follicle cells. We have here very clearly the beginning of the 

 formation of the permanent sex-gland. 



The changes of the germ-cells themselves at this period are 

 well marked. A group of these cells is shown in fig. 34, three of 

 which have changed considerably while the remaining two are 

 still in the condition common in the earlier period. The nucleus 

 is no longer irregular and shrunken in appearance, but has become 

 round and full and is much larger than that of the earlier cells. 

 The actual size of the whole cell has changed little, if at all, so 

 that the nucleus occupies a much greater proportion of the cell 

 space than before. Another conspicuous change is the thicken- 

 ing of the chromatin-linin reticulum; this causes the nucleus to 

 stain more deeply. The two plasmosomes of former stages have 

 now become fused into one single mass and its total volume has 

 increased very considerably. These changes are probably to be 

 followed shortly by cell division, so that in embryos a little older 

 we should expect to see many of these cells in mitosis. These 

 cells are evidently the primary oogonia (or spermatogonia) as 

 direct descendants of which the functional sex-cells of the mature 

 fish arise. 



* A prominent feature of the drawings of these stages, also prominent in the sec- 

 tions themselves, is the large amount of dark brown or black pigment. Pigment 

 cells may be distinguished as early as stage 7. From this time on pigment steadily 

 increases in amount, till at the time of hatching it is a very prominent feature of 

 the young fish. (figs. 17 and 18). 



JONRNAL OF MOHPHOLOGT, VOL 21, NO. 4. 



