58 SUMMAEY OF CL'EKENT RESE.AJiCHES EELATIXG TO 



Experiments were also made bv removing the testis of a rat and 

 substituting another, or part of another, from another animal, but 

 there was no positive result to prove that the implanted testis survived. 

 It seems that testicular tissue is much more sensitive to injury, me- 

 chanical or otherwise, than is ovarian tissue. 



(xenn-cells of Man and Mammals.* — A. Fuss discusses the origin 

 of the germ-cells in the embryo. They were to be seen in a human 

 embryo 2 • 5 mm. in length, partly in the endodermic epithelium, panly 

 in the mesoderm. There is evidence pointing to amceboid movement. 

 In a human embrvo of about four weeks a few were still in the vicinitv 

 of the primitive gut, but most were in the dorsal mesentery near the 

 aorta. Besides active amceboid migration there is passive transport by 

 the growth of tissues. The germinal epithelium does not enter into 

 proliferation until the majority of the germ-cells have reached that 

 region, after thirteen days in the rabbit, after the fourth week in man. 

 The future germ-cells are descended from the migrants, not from the 

 germinal epithelium. 



Spermatozoa of Aard-Vark.t — E. Ballowitz describes the sperma- 

 tozoa of Orycterojju-s afer, and notes that, contrary to his exp>ectation, 

 they are not in any way divergent from the ordinary Mammalian type. 

 In the characters of the head, the middle piece and the tail, there is 

 nothing noteworthy — a striking contrast to what Ballowitz found in 



JllVlhS. 



Fibres of the Zonula.; — W. M. Baldwin has investigated the develop- 

 ment of the fibres of the zonula zinnii in the white mouse. They arise 

 from mesenchyme cells, and are at first attached to the apical processes 

 of the cells of the internal cUiary epitheUum. Later on, the zonula fibres 

 change their attachment and penetrate into the intercellular substance 

 which Lies between the cells of the internal ciliary epithelium. In the 

 fuUy developed eye the zonida fibres penetrate the intercellular substance 

 towards the limitans ciliaris externa, but they end abruptly before they 

 reach this. They end only at that part of the ciliary epithelium, which 

 lies in the valleys between the ciliary processes and the ora serrata. 



Primitive Sex-cells in Chick Embryo.§— H. vou Berenberg-Gossler 

 notices that the proof that *' the primitive sex-cells " in the very young 

 chick embryo are primitive sex-cells is not qtiite satisfactory. They are 

 brought into the genital region, not by amoeboid migration, but along 

 with a large complex of the visceral plate of the mesoderm. The move- 

 ment is a consequence of the closing of the gut into a tube and the 

 formation of the mesentery. The particular features in these cells, which 

 mark them off from other embryonic cells, are not essential ; they are 

 rather due to the absence of function and cell-division in these early 

 stages (third to fourth day of incubation). 



* Arch. Mikr. Anat., Ixixi. (1912) Heft 1, Abt. 2, pp. 1-23 (2 pis. and 5 figs.). 



+ Anat. Anzeig., xlii. (1912) pp. iS2-6 (6 figs.). 



t Arch. Mikr. Anat.,lxxs. (1912^ pp. 274-305 (2 pis.). 



§ Arch, ilikr. Anat., Ixxxi. (1912) Heft 1, Abt. 2. pp. 24-72 (1 pi.). 



