84 The Rete-Cords and Sex-Cords of Chrysemys 
necessary to first understand certain features in the development of the 
mesonephros. Reference to these features will be made only in so far as 
they concern the subject of this paper. In an early stage of develop- 
ment (C-7. 3.5 mm.), a section through the posterior part of the sex- 
gland fundament shows the mesoblastic somites to be attached to the 
lateral plates by the unmodified middle plate (Text Figure #). The 
cells of the latter are arranged in two rows, in such a manner as to leave 
a line of weakness between, which may be considered as a rudimentary 
lumen, connecting the body-cavity on the one hand with the cavity of the 
Text Fic. E. Transverse section through the middle of the mesonephros 
fundament of an embryo of 3.5 mm. C-T. length. 
AO.— Aorta. NO.—Notochord. 
EC.—Ectoderm. SO—Somatopleure. 
MY.—Myotome. SP.—Splanchnopleure. 
N.—Neural canal. WD.— Wolffian duct. 
NEP.—Nephrotome. 
mesoblastic somite on the other. In the region posterior to this, these 
relations become even more marked. 
More anteriorly, just behind the interesting region which forms a 
transition between the pronephros and mesonephros, the middle plate is 
found to be wholly broken away from the mesoblastic somites, and to be 
divided by transverse intervals into nephrotomes which occur in the 
number of three to four per somite. 
I found no evidence of a primary metamerism of these nephrotomes. 
So soon as the middle piece appeared to be broken up at all, the number 
of nephrotomes here recorded appeared. Special investigation along this 
