The pronephros of Chryseinys niarginata. 17 



some places, and apparently in close relation with the ectoderm 

 posteriorly). If one notices the groove of the ectoderm into which 

 the kidney rudiment extends throughout the pronephric region, one 

 can understand how it may easily be supposed that the unformed 

 posterior end of the pronephric duct arises from the ectoderm, 

 although this is not really the case. 



The segments affected are: post, portion of V, front end of VI, 

 VII, VIII, IX and X. The duct is present in XI, XII and 3 sections 

 further back, 



(See Plate 1 Figs. 11, 12, 13, 14, 15.) 



On the right side the outgrowth is probably present at and about 

 3,13, but at 3,20 it is prominent, and continues back to 3,45; the 

 duct begins at 4,1 and ends about 4,21. 



Segments affected are VI?, VII, VIII, IX; the duct extends 

 over X and XL 



Embryo F. 



Stained for 48 hours in Geenacher's Boraxcarmine. Counted 

 12 or 13 protovertebrae after clearing in xylol. Six slides used, 

 upon which 45, 45, 45, 45, 39, and 39 sections were mounted re- 

 spectively. This embryo was strongly twisted at the front end, 

 and 1 had some difficulty in counting the anterior protovertebrae. 



The heart is just becoming a twisted tube. 



Body begins 1,3. 

 Left side of embryo Right side of embryo 



