ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 361 



Staining nucleoli which fuse before activity is marked ; the result is 

 possibly the X-chromosome or associated therewith. The spermatogonia 

 show twenty-one oval chromosomes. Following the spermatogonial 

 division the chromosomes weave out into separate leptotene threads, 

 while the X-chromosome remains as a rounded or slightly oval dark- 

 staining mass. The leptotene threads undergo parasynapsis. Eleven 

 chromosomes appear in the primary spermatocyte, ten are bivalent 

 autosomes, and one is the X-chromosome. The X-chromosome passes 

 undivided to one pole while the autosomes divide by longitudinal split- 

 ting. Thus there are produced two kinds of secondary spermatocytes, 

 the division being a reducing division. These two kinds of secondary 

 spermatocytes give rise by division to two kinds of spermatids, one with 

 ten univalent autosomes, the other with ten univalent autosomes and 

 the X-chromosome. During spermiogenesis the centrosome gives rise 

 to the end knob, axial filament and the posterior centrosome ; the sphere 

 substance of the secondary spermatocyte division to the acrosome ; and 

 the spermatosphere to the sheath of the middle piece. Measurements 

 of mature spermatozoa give a distinct bimodal curve, also indicating 

 their dimorphism. J. A. T. 



Idiosome in Spermatogenesis of Guinea-pig. — George N. Papa- 

 nicolaou and Charles R. Stockard {Amer. Journ. Anat., 191<s, 24, 

 37-69, 2 pis.). The idiosome in the spermatogonia is very variable. 

 In the primary spermatocytes it shows an internal idioendosome sending 

 processes into a larger surrounding idioectosome. When the primary 

 spermatocytes prepare to divide the idioendosome breaks into granules 

 (idiogranulomes), which by the breaking up of the idioectosome are 

 scattered in the cytoplasm. They reunite after division, forming a 

 granular idiosome in the secondary spermatocytes. This breaks up as 

 before and a reconstruction occurs in the spermatids, in which each 

 idiograuulome in the idiosome appears to be surrounded by a minute 

 vacuole, the idiogranulotheca. They run together until there is one 

 large granulome, the idiosphferosome, surrounded by one large vacuolar 

 wall, the idiosphierotheca. The subsequent differentiation of the sperma- 

 tozoon is described in detail. During all stages there are a number of 

 granules in the nucleus, karyogranulomes, which eventually seem to be 

 dissolved within the sperm-head in the same'way as the chromatin. The 

 role of granulation is probably to secure a distribution of the idio- 

 plasmatic substance during cell-division. J. A. T. 



Development of Red Blood Corpuscles. — Vera Danchakoff 

 {Aiuer. Journ. Anat., 191S, 24, 1-32, 1 pi). The differential factors 

 in the development of a polyvalent cell are extrinsic, and in the erythro- 

 blastic differentiation of a hgemoblast depend on the conditions present 

 within the vessels. These factors are active not only in the lower 

 vertebrates, in which normally no extravascular erythropoiesis is 

 observed, but the same factors seem to determine the erythropoiesis in 

 mammals (erythropoiesis in embryonic early stages and experimentally 

 produced in the adult), rendering the derivatives of the hremoblasts, 

 the erythroblasts, specific — univalent and irreversible in development. 



