390 WALTER E. CAMP 



the development (28 to 33 mm.) the blind ventral extremity of 

 the tubule expands into a small vesicle which becomes bent in 

 a medial and cranial direction. This bending of the gland and 

 its extension medially and cranially, which becomes very promi- 

 nent in the older embryos, is probably due to the resistance 

 offered by the dorsaJ pericardial wall. The cells lining the 

 pharynx at this stage are cubical or low columnar and have 

 broadly oval nuclei (fig. 9) . In the region of the pharynx lateral 

 to the gland, the epithelium possesses a double row of rounded 

 nuclei. Although not shown in the figure, the cavity of the 

 connecting-stalk communicates with the pharynx and the dilated 

 vesicle, both of which are lined by columnar cells with regular 

 oval nuclei. 



The gland remains in this condition, becoming somewhat 

 larger and more expanded, up to about the 36-37 mm. stage, 

 when it is somewhat variable in its finer structure. It usually 

 shows a solid connection with the pharynx and its ventral por- 

 tion becomes more or less separated from the connecting-stalk. 

 Both the vesicle and the tortuous connecting-stalk show the 

 beginning formation of new tubules. Often the larger expanded 

 vesicle has already become divided up into two or three smaller 

 independent ones, which also show the formation of new tubules. 



Since the further growth of the gland from this time up until 

 about the newborn stage, consists chiefly of the multiplication 

 and branching of the gland elements, i.e., the tubules — this 

 process will be considered in detail. The bulk of the small 

 newly formed tubules always occurs between the ventral vesicle 

 and the epithelial wall of the pharynx, showing that in all prob- 



Fig. 8 Transverse section through the left suprapericardial body and phar- 

 yngo-pericardial wall of an embryo 20.6 mm. long (H. E. C. 149-4); iron hacma- 

 toxylin. X 525. P., pericardium. 



Fig. 9 Transverse section through the left suprapericardial body of an em- 

 bryo 33.1 mm. long (S. C. 8); alum hematoxylin. X 400. C.s., connscting- 

 stalk; 1'., vesicle; P., pericardium. 



Fig. 10 Transverse section through the cranial portion of the left supraperi- 

 cardial body of an embryo 47.3 mm. long (S. C. 11); alum hematoxylin. X 285. 

 A., B., C, remnants of early connecting-stalk; D., ventral cyst, showing two 

 small buds on its right border. 



