ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 379 



Development of Milk-teeth of Aard-Vark.*— Paul Heuser finds that 

 all the priniordia show a more or less well-developed enamel organ, and 

 that apart from the early atrophy of the enamel pulp they do not differ 

 from typical Mammalian primordia. He found fourteen primordia on 

 each side below, and twelve above. The resemblance between Orycte- 

 ropus and Dasypus as regards the early atrophy of the enamel pulp is 

 emphasized. 



Early Stages in Development of Grass-snake.t — E. Ballowitz 

 points out that the forerunner of the blastopore plate in Tropidonotus 

 natrix is the " marginal sickle " which appears at the posterior end of 

 the embryonic shield. It is visible to the unaided eye as a narrow, 

 whitish, non-transparent curved ridge, with the concavity forwards. It 

 is soon accompanied by the transitory flat archistome-groove, with the 

 same curvature as the sickle. Under the shield and the blastoderm 

 there is a layer of yolk-entoblast. The cell-material of the marginal 

 sickle and the subsequent blastopore plate is due not only to the shield- 

 ectoderm, but to an accession of yoik-entoblast as well. In this mixed 

 cell-material there is abundant mitosis, leading on to the formation of 

 the blastopore-plate. 



h. Histology. 



Amitosis in Epididymis of Mouse. J — H. E. Jordan finds that 

 amitosis is the exclusive method of division of the ciliated epithelial cells 

 of the epididymis of the white mouse. In the vasa efferentia, due 

 mainly to the larger size of the cuboidal cells, the complete process can 

 be followed with absolute precision. Every possible phase is seen. There 

 is no regularity with respect to the orientation of the nucleus in the 

 cells, nor uniformity as to the plane of division with respect to the shape 

 or position of the nucleus. In the vas epididymis the relative number of 

 amitoses is slightly reduced. Not a single mitotic figure appears. Basal 

 granules and marginal plates are present throughout the epididymis. 



Jordan's observations on the white mouse, supplemented by others 

 on the epididymis of rat, horse, bull, mule, rabbit, and dog, and on the 

 trachea of the cat and the ciliated cells of the gill of Unio, lead him to 

 conclude that the fundamental cause of amitotic division in ciliated 

 cells is the destruction of the centrosome in the formation of the basal 

 bodies from which the cilia develop. As Child has suggested, amitosis 

 may signify a lack of adequate nutrition, but the point of incidence of 

 the nutritive inadequacy is the centrosome of the cell. 



Peculiar Forms of Cell in Tongue-epithelium of Guinea-pig-.i 



Christian Ditlevsen describes narrow, curved, spindle-like cells, with 

 elongated nuclei and with a strong affinity for basic nuclear stains. 

 They occur in many guinea-pigs but not in all. They do not appear 



* Zeitschr. wiss. ZooL, civ. (1913) pp. 622-91 (2 pis.). 



t Zeitschr. wiss. ZooL, cv. (1913) pp. 178-91 (2 pis. and 2 figs.). 



X Anat. Anzeig., xliii. (1913) pp. 598-612 (43 figs.). 



I Anat. Anzeig., xliii. (1913) pp. 481-500 (5 figs.). 



