506 SUMMARY OF CURRENT RESEARCHES RELATING TO 



intervenes between the first and second divisions, during which in- 

 dividualised chromosomes are no longer to be distinguished. The only 

 marked differences from the salamander are the completeness of the rest- 

 stage in the rat, and the occurrence of ring-chromosomes in the second 

 as well as in the first division. The author considers that all the 

 evidence is against the view that the germ-cells contain individualised 

 chromosomes which are the bearers of the hereditary qualities, and 

 persist unaltered throughout the generations of the sex-cells ; but this 

 does not shake the main generalisation that the chromatin is the bearer 

 of the hereditary qualities. 



Spermatogenesis in the Domestic Sparrow.* — Gustave Lois el sums 

 up his observations on the early stages of this process. He finds that 

 the germinal epithelium of Waldeyer does not disappear in the early 

 stages of the development of the testis ; it persists in the young bird, 

 or even in the adult, in the form of cells which may be called the 

 germinal cells. These cells constitute the source of all the sex-cells, 

 but diminish in number and activity as the period of spermatogenesis 

 approaches. The spermatogonia are derived from these germinal cells, 

 and are capable of multiplying by both direct and indirect division. 

 These divisions are fewest in the early stages when the germinal cells are 

 most active, and most in the later stages when the germinal cells divide 

 little if at all. The result is that at the end of the period of pre- 

 spermatogenesis, the generative zone of the seminiferous epithelium 

 consists only of spermatogonia. From the time when, in the embryo, 

 the spermatogonia of the second order appear until the formation of 

 perfect spermatozoa in the adult, the testis does not remain in a condition 

 of rest, but shows a periodic production of cells of an advanced type, 

 followed by a period of regression during which these cells degenerate 

 and are absorbed. Certain of the elements produced during each pro- 

 gressive period persist through the following regressive period, so that 

 each period constitutes a step forward. When the periods succeed one 

 another rapidly, then the functional activity of the testis begins. 



Uniformity of the Embryos of Primates-t — Prof. E. Selenka com- 

 pares various stages in the development of man, gibbon, Cercocebus 

 cynomolgus, Semnopithecus, &c, and shows the very close resemblances 

 between them, both in the early and later stages. To take a single 

 example ; — he observed in the embryo of Cercocebusc ynomolgus a sharp 

 dorso-ventral indentation towards the posterior end of the trunk, which 

 afterwards disappears ; it is a striking feature never seen except in 

 Primates ; it has been described in man about the loth or 16th day. 



Retrogressive Changes in Embryonic Primordia.J — Prof. M. Nuss- 

 baum describes the structure, the rise, and the retrogression of the 

 papillaB of the conjunctiva sclerse which appear in the chick embryo 

 towards the end of the sixth day of incubation, and compares the 

 primordia of these structures with the first primordia of the feathers, 

 showing that, as regards the role of the connective-tissue for instance, 

 there is very little in common between them. Are the transitory papillae 



* Journ. Anat. Physiol., xxxvi. (1901) pp. 193-216 (2 pis.). 

 + Biol. Centralbl., xxi. (1901) pp. 484-90 (19 fiss.). 

 X Arch. Mifer. Anat., lvii. (1901) pp. 676-705 (3 pis.). 



