290 N. M. Stevens. 



in the cytoplasm during or after each mitosis. In Fig. 56, 6 is a 

 cell in prophase and a two recent products of mitosis. The rest- 

 ing nuclei of oogonia often show as many granules in tangential 

 section as in Fig. 57 or 58, but it is in the young oocytes at the 

 very beginning of the growth stage that one finds relatively large 

 masses of this chromatin-like material inside the nuclear mem- 

 brane. It most often lies at the two ends of an elongated nucleus, 

 and several of the chromosomes are closely associated with it 

 (Fig. 59). In Fig. 60 one of these masses has begun to divide. 

 Figs. 61 and 62 are nuclei of slightly older oocytes with the large 

 masses broken up into smaller ones, and the volume of these in- 

 tranuclear granules is also apparently increased. Fig. 63 is a 

 tangential section of a somewhat later stage showing the begin- 

 ning of the network which replaces the masses and granules in 

 older oocytes. These granules, as well as the reticular network, 

 stain like the chromosomes with iron-hsematoxylin, borax carmine, 

 saffranin, and Benda's stain for mitochondria. Figs. 64 and 65 

 show the characteristic network which lines the nuclear membrane 

 of older oocytes of Sagitta bipunctata. The pattern consists 

 of two parts, the network and the irregular figures in the open- 

 ings. These two parts vary in prominence in different species. 

 In Sagitta bipunctata the meshwork is more prominent, and in 

 older eggs the central figures disappear first. Figs. 66 a and b 

 are tangential and median sections of the same nucleus. Figs. 67 a 

 and b similar sections of the nucleus of an older egg, showing the 

 breaking up and gradual absorption of the network as the egg 

 approaches maturity. When the chromosomes have been re- 

 duced to the maturation size, the stainable network has practi- 

 cally all disappeared from the nuclear membrane (Fig. 68). In 

 Sagitta minima, one finds in young oocytes stellate or amoeba- 

 like figures (Figs. 69 and 70) , which later unite to form a network 

 (Fig. 71), which may or may not have rather indistinct figures 

 in the spaces (Fig. 72). In Sagitta infiata I usually find such a 

 pattern as in Fig. 73, and Fig. 74 from an older egg. In these 

 three species the network is more prominent than the contained 

 figures. In Sagitta elegans it is the reverse — the central figures 



