Arthur W. Meyer 259 



tures with small necks and large distal ends, which in embryos of nine 

 weeks are branched and are found in all parts of the mesoderm 



and fat oft '^'rW''' '''''' '' '^*^™^°^' '' P^^^^^^' ^^e origin 

 and fate of these glandular structures, and to throw some light m^n 



their possibe function. So far as I have been able to learn, Graf Spee 



was the first to mention and to describe them, and no one else seems to 



have suggested any explanation of their presence. These glandular 



structures which for the sake of brevity I shall call tubules, are present 



m the walls of nearly all vesicles taken from embryos less than two 



months old m the collection of Dr. Mall. The vesicles of A^s. n and 



U of this collection, embryos 0.8 mm. and 2.1 mm. respectively, are 



Identical in structure. Both are in a state of good preservation, and 



their structure m cross section as represented in Fig. 1. 



bloodvessel 



FIG. ]. Umbilical „siole ot ,„ embrjo 2.1 mm. long ,N„. 12,. x 35, 



narr''ow'll,','f '" " 'T/T"' *"'' ^"^P'^' »^"°'J'-^' ^bules with 



1 / , f , - " '" **'" mesoderm close to the entoderm. These so- 

 called glandular stn^ctnres do not branch and can be traced throng from 



fo.fn;r;h:tsLL':';tr;To''t '""^^ ^'^'"^ °' '-- *"^-- '^ 



Here thf. ,„„„1 f * , ' ' ™'"'^° '''™ millimeters long. 



Here the number of tubules is considerably greater and a direct connec- 

 .on be ween many of them and the entoderm exists (Fig. 2). In many 

 a es the tubules end as evaginations of the entoderm "and arc thr^n 

 direct communication with the cavity of the vesicle. Others are "nd" 

 r^ly connected with the entoderm by bands of entoderma Icel ^ht 

 s 111 others he isolated m the mesoderm. As showu in Fig. 3 all transi 

 ions are found from a slight evagination of the entoderm t los d 

 ubules lj.ng detached from the entoderm in the mesoderm. Altl gh 

 they can be traced through a series of fifteen to twenty-five sections Z 

 are never seen to branch. On the other hand the branching described by 



