HALL : MESONEPIIROS AND MULLERIAN DUCT IN AMPHIBIA. 51 



forming the covering of the glomerulus. In Amblystoma, at least, it is 

 only the median portion of the wall of the invagination (cjjs. Bow. i.) 

 which forms the glomerular covering, the lateral wall (thl. ms'nph.) 

 allying itself entirely with the inner tubule. 



The further development of the Malpighian body is as follows : the 

 median wall of the infolding (cpa. Bow. i., Fig. 23), which is conspicu- 

 ous as the most darkly staining portion of the entire unit, grows dor- 

 sad, stretching the tissue of Bowman's capsule {cps. Boiv.ex.) to a very 

 tliin membrane. It then becomes curved to form a hollow hemisphere 

 with the convexity directed toward the capsule, thus reducing the lumen 

 of the latter to a narrow slit. The cavity of the hemisphere then becomes 

 filled with cells, which increase in number until the whole forms a com- 

 pact, darkly staining mass, the glomerulus. I am not certain as to the 

 origin of the cells which fill the glomerulus. They may arise in situ, 

 but I am inclined to think they are derived from small masses of cells 

 which lie beneath the aorta, as there is often seen a connecting cord of 

 cells between these masses and the glomerulus. 



In Figure 23 the curves of the inner tubule all lie approximately in 

 one plane. With increase in length, its curves become more complex 

 and are no longer confined to the transverse plane. Figures 34 and 35 

 (Plate 3), drawn from a wax reconstruction, show a stage in which the 

 curves are still rather simple. The mesonephric unit in this case is 

 from the eleventh somite of a larva 16 mm. in length and is almost 

 functional (see Explanation of Plates). A comparison of Figure 34 with 

 Figure 23 will show that the cone of cells (iipli'stm.) connecting the 

 unit with the peritoneum becomes the outer tubule. This later elon- 

 gates somewhat. 



At the point crv. cp, Mp)g. (Fig. 23) the outer and inner tubules com- 

 municate with the lumen of the Malpighian body. In forms more 

 primitive than the Amphibia, this condition persists. In Myxine (Maas, 

 '97) the outer tubule may even open into the cavity of the Malpighian 

 body at a point opposite the opening of the inner tubule. In Amblys- 

 toma, however, as in Ichthyophis (Semon, '92), the outer tubule appar- 

 ently loses its direct connection with the Malpighian body and opens into 

 the inner tubule at a short distance from the opening of the latter into 

 the Malpighian body (Plate 3, Fig. 24, crv. cp. Mpg.). This is brought 

 about by a constriction of the Malpighian lumen just mesal to the point 

 marked crv. cp. Mpg. in Figure 23, combined with a lengthening of the 

 constricted region. The short, ciliated tube thus formed, which I shall 

 call the neck of the Malpighian body, has generally been considered a 



