Further Studies on Reproduction in Sagitta. 295 



fiata, as one looks down into the gastrula cavity. Fragments of 

 the 'besondere Korper' are found only in the two cells with the 

 smaller nuclei which are the products of the later mitosis. In the 

 stage shown in Fig. 51, 1 am unable to detect any constant differ- 

 ence in either cytoplasm or nuclei of the cells, and even in young 

 ovaries and testes consisting of a single cell (Figs. 1 to 3) or con- 

 taining a number of oogonia or spermatogonia, the cells are so 

 much alike than one must depend upon other anatomical features 

 to determine whether one is looking at a section of a young ovary 

 or a young testis. 



Intranuclear Granules and Network 



In my- 1903 paper I referred briefly to certain large black gran- 

 ules found on the inside of the nuclear membrane of young oocytes, 

 and also to the ''reticular network" conspicuous in the nuclear 

 membrane of all older oocytes up to the time when the egg mem- 

 brane forms. While I was working on the development of the 

 sperm-duct and oviduct in Professor's Boveri's laboratory, he sug- 

 gested that it might be interesting to investigate the origin of this 

 network in view of its possible relation to the mitochondria recently 

 described in the cytoplasm of many kinds of cells. At the time 

 I could not trace it back farther than the young oocytes, perhaps 

 a little younger than those shown in Figs. 4 and 6, PI. 1, '03, and I 

 thought it desirable to examine more carefully than I had pre- 

 viously done the embryonic and larval stages of the germ cells, 

 with this question in mind. Sections of those, however (Figs. 

 1 to 3, 46 to 52) , throw very little light on the point. The ero.bry- 

 onic germ cells show some granules, but nothing really comparable 

 to those of the young oocytes. The oogonia of young ovaries 

 show several rather large granules, or chromatin-nucleoli, against 

 the nuclear membrane (Figs. 8 and 10). Dividing oogonia also 

 show these nucleoli outside of the spindle in both metaphase 

 (Fig. 53) and anaphase (Figs. 54 and 55). In the daughter nuclei 

 no such nucleoli are found, and it therefore seems probable that 

 these chromatin-nucleoU consist of material thrown out by the 

 chromosomes in the interval between two mitoses, and dissolved 



JOURNAL OF MORPHOLOGY — VOL. 21, NO. 2 



