56-8 SUMMARY OF CURRENT RESEARCHES RELATING TO 



with vessels and glands. These pillars pass into a broad maternal sub- 

 chorial layer with large glandular spaces. In the musculature of the 

 uterine wall there is a close network of maternal blood-spaces, almost 

 like a corpus cavernosum, and from this some small vessels pass towards 

 the inter- villus space, which contains abundant maternal blood, and others 

 into the mucus-membrane pillars. 



Formation of Mesoderm in Mammals.*— R. Tsukaguchi has 

 studied this in goat and rabbit. The first primordium of the mesoderm 

 appears very early, before there is any primitive streak. It is marked 

 by several thickenings of ectoderm at the caudal part of the shield, from 

 which the mesoderm-germs are gradually segregated off. They take 

 some share in forming the " Mesodermhof ." In the goat they spread 

 over the whole shield-margin, forming an annulus ; in the rabbit the 

 primordium is more restricted to the caudal area of the shield and 

 shares in forming a " Mesodermhof " in tlie vicinity of that area. 



Development of Thymus in Duck.f — B. Hamilton finds that the 

 thymus of the duck is a purely endodermic thymus, arising cliiefly from 

 the caudal wall of the third gill-pouch. The third parathyroid arises 

 from the lateral portion of the cranial wall of the same pouch. Even- 

 tually the thymus is dorsal to the pouch and the third parathyroid 

 ventral. On the dorsal wall of the first and second gill-pouch, there is 

 a transitory epithelial proliferation. The fourth parathyroid arises from 

 the lateral portion of the fourth gill-pouch, and with the median por- 

 tion of the same pouch the " post-branchial body " is connected. 



Pronephros of Chrysemys marginata.J — T. H. Buriend has 

 investigated the early development of the kidney in the American 

 Terrapin, and comes to the following conclusions. The rudiment of the 

 kidney in Chrysemys is in the form of a continuous "primitive kidney 

 groove," arising as a somatopleuric evagination of the mesoderm of the 

 lateral plate region. This primitive condition is less evident farther 

 back (in the middle region of the pronephros), where it assumes rather 

 the form of a solid thickening of the somatic mesoderm. From this 

 rudiment arise by later modification both the anterior kidney tubules 

 and the front part of the pronephric duct. There is evidence that the 

 '• primitive kidney groove " extended farther forward in the ancestors of 

 Chrysomys^ since remains of this organ are found as far forward as 

 segment iii. The pronephric duct is of mesodermal origin, although 

 contiguous with the ectoderm for some distance in its middle region : 

 intersegmental proliferations of mesoderm probably reinforce its ])ack- 

 ward growth, though the rudiments of the duct appear before these 

 proliferations reach it in any particular region. The appearance of the 

 duct precedes the appearance of the posterior pi'onephric tubules by a 

 short, and the anterior mesonephric tubules by a longer interval. The 

 pronephros attains its fullest development in segments vii-x, and 



* Anat. Anzeig., xliv. (1913) pp. 513-19 (1 pi.). 



t Anat. Anzeig., xliv. (1913) pp. 417-39 (13 figs.). 



X Zool. Jahrb., xxxvi. (1913) pp. 1-90 (4 pis. and 12 figs.). 



