ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 569 



probably extends into segments xi and xii (?) also. The pronephric 

 duct passes into the gut in the region of the primitive groove (blastc- 

 pore). Tt becomes hollow from before backwards. 



The mesonephric tubules appear, without any appreciable break in 

 time, and no break in space, behind the pronephric ; their difference in 

 structure is entirely due to their different envh'onment. The difference 

 in the mesonephric rudiment (as compared with the homologous prone- 

 phric) is due to a rotation of both duct and kidney structures. This 

 rotation through an angle of more than 90° changes the position of the 

 pronephric duct from a dorsal to a lateral position, relatively to the 

 pronephros, and also results in a change of position in the mesonephric 

 tubules so that they become dorso-median with respect to the duct. 

 The nephrostomes likewise from being ventral and coelomic, become 

 median and nephrotomic. This rotation is not of equal extent in 

 the individual segments, being most complete in the middle of each 

 segment, and less pronounced at the ends. There is evidence that the 

 original pronephric nephrostomes divide up into a number of smaller 

 ones, and so tend to multiply the number of nephrostomes to a tubule : 

 this tendency in the mesonepihric tubule is the probable cause of the 

 so-called secondary, tertiary, etc., mesonephric tubules. The region of 

 the nephrotome into which each mesonephric tubule opens becomes 

 enlarged to form a Malpighian capsule. The vascular supply to the 

 anterior region of the kidney is in the form of a continuous out-growth 

 from the aorta, and this projects as a glomus into the coelom. The 

 rotation and metamerism affect the glomus in the posterior part of the 

 pronephros, and in the anterior part of the mesonephros, and so the 

 glomus is represented in these regions sub-divided into glomeruli. The 

 blood-supply develops after the tubule formation. Later modification 

 of the mesonephric growth consists in the branching of the primary 

 glomeruli ; fusion, in places, of vascular tissue with the nephrotomic 

 wall between the tubule nephrostomes leads to the subdivision of the 

 nephrotome into Malpighian capsules, and so to an increase in the 

 number of Malpighian capsules with glomeruli and nephrostomes. 



Development of Skull of Anguis frag-ilis.* — S. Zimmermann gives 

 an account of the formation of the chondrocranium in the slow-worm, 

 and figures his reconstructions made on the Born-Strasser plan. It is 

 interesting to notice that even the chondrocranium differs in some 

 respects from that of Lacerta. 



Spermatogenesis of Amphibians. t — Christian Champy has made 

 an elaborate study of the spei'matogenesis in various Anura and Urodela. 

 Some of the more importaut results may be cited. 1. The seminiferous 

 tubules of Anura are not quite stable structures. They are formed 

 somewhat late ; their boundaries become vague at certain times of year. 

 The follicular cells are not distinct from the interstitial cells till very 

 late in development, and the distinction is not constant. 2. There is 

 in Batrachians a prespermatogenesis before the advent of sexual maturity, 



* Anat. Anzeig., xliv. (1913) pp. 594-606 (5 figs.). 



+ Arch. Zool. Exper, lii. (1913) pp. 18-304 (12 pis. and 104 figs.). 



