352 FREDA M. BACHMANN. 



the individual cells in a nest in proportion to the size of the nest, 

 good proof that no epithelial cells are transformed into germ 

 cells. The nests of cells are at first some distance apart and be- 

 come nearer together as the cells increase in number by division 

 not as new cells are formed from epithelial cells. 



MacLeod ('81) in Hippocampus and Belone acus observed that 

 the sex cells appear in the somatopleure and splanchopleure 

 rather late in development and thought them to be differentiated 

 peritoneal cells. He thought the genital fold originates in a 

 group of germ cells on the surface of the epithelium. 



Hoffmann ('86) studied salmon embryos. According to him 

 the genital glands have their origin in the primary germ cells 

 which are first found in the median and dorsal part of the mesen- 

 tery and laterally to the body wall. He could see nothing more 

 in these germ cells than transformed and highly differentiated 

 peritoneal cells which in the youngest stages of development 

 increase in number by mitosis. Later these cells come to lie 

 laterally from the mesentery and extend into the body cavity as 

 a small fold. The cells increase in number by division and trans- 

 formation of more peritoneal cells. Nests of germ cells are thus 

 formed. Later each cell becomes surrounded by follicle cells. 

 He could not say whether these follicle cells are connective tissue 

 cells or of epithelial origin, i. e., from a germinal epithelium. 

 However, he inclined to the latter because the follicle cells appear 

 before a connective tissue stroma is differentiated. 



Bohi ('04) worked on the trout and the salmon. In the trout, 

 twenty-five days after fertilization and six days later in the 

 salmon, he found large cells among the larger epithelial cells in 

 both the somatopleure and splanchopleure. The cells have very 

 large nuclei but no nucleoles. The cytoplasm stains lightly and 

 is without definite structure. The nuclear content is granular 

 and hence takes little of the stain. The cells are more oval or 

 ovoid in younger embryos and rounder in older ones. There is 

 a diminution in volume before division begins. There is a 

 definite relation between the size of the nucleus and the size of 

 the cell the large cells always have the larger nuclei. In two 

 trout embryos of twenty-five days he found in the lateral plate 

 four and six germ cells respectively. In salmon embryos of 



