Susanna Phelps G-age 423 



of tubules described above are all lost. The 17 to 18 tubules are complete 

 and like Fig. 19. 



In brief, there is, in human embryos, of the 17th to the 23d day, the 

 history of the origin of the tubules from a cellular blastema. This 

 blastema segments into rounded masses, these masses develop cavities that 

 first unite with the cojlomic epithelium, then losing this connection, 

 unite with the Wolffian duct which already had definite enlargements, 

 and then finally each tubule forms the thin-walled Bowman's capsule with 

 its glomerulus. 



The connection which probably existed between the myotomes and the 

 coelom through the intermediate cell mass which gives rise to the blastema 

 forming the tubules, is of an earlier stage than these here considered. 

 Dr. Minot in the discussion of this paper when presented at the meeting 

 of the American Anatomists stated that in a very early rabbit in the 

 Harvard University Medical School collection, such connection can 

 actually be seen between myotome and nephrotome to the coelom. I have 

 recently seen the same in the chick. 



Metanephros. — If any trace of the metanephros or true kidney exists 

 in specimen No. 148, it consists merely of a slightly condensed portion 

 of the blastema, caudad of the mesonephric region where the Wolffian 

 duct extends beyond the coelom (Fig. 17). 



Central Nervous System. 



General. — Most of the figures illustrate some features of the central 

 nervous system. The general outline follows closely the profile shown in 

 Fig. 1. The lateral and mesal views are seen in Figs. 3, 4, and with 

 segments of the model and photographs of the sections together give 

 better than words, the idea of shape. The form more nearly approaches 

 that of embrj'o Lr (4.2 mm. long, with 32 myotomes) shown in His's " 

 atlas (Plate IX, Fig. 13), and the model of the same than any other 

 specimen figured. 



The stage of development of eye, olfactory pit, and ear vesicle also put 

 it in the same class, that is, the nervous system is like, in general features, 

 this well-known specimen of three weeks. Details which bear upon the 

 object of the present investigation are not shown by His nor, as far as f 

 know, by other writers on mammalian brains. Mall ^ in an early presen- 

 tation of this same embryo mentions the neuropore, which in the present 

 article is fully illustrated and in a way made the starting point for 

 definite conclusions. 



The evidence from human and mamnialian as well as immammalian 

 33 



