00 J)i'vol(>puu'nt and Shape of T'rinifVrous Tubules 



zone, others (the ])i-()i)()i-ti()ns 1 am not al)le to give) remaining entirely 

 within the mediiUary rays. A\'liat has been said of. the upper end of 

 the descending liml) of the loop of Henle applies also to the upper end 

 of the ascending limb. The junctional tubule passes through the cortex 

 between the rays until it ai'ches over to reach the collecting tubule in 

 which it terminates. 



I have in connection with Figs. 21 and 22 spoken of the relations, as 

 seen in sections, shown by the coil complex and the jMalpighian cor- 

 puscles of any given tubule. A study of the sections from which the 

 models were made has not enabled me to formulate any general law 

 concerning this relation. This depends, as may readily be seen, even 

 in what may be regarded as very favorable sections, entirely on the 

 direction of the sections. Frequently the greater part of the coil com- 

 plex formed by the proximal and distal convoluted portions of a given 

 tulnile may be cut in a series of sections without cutting the ]\Ialpighian 

 corpuscle of said tubule. The relations of coils of juxtaposed tubules is 

 such that one or more of the loops, especially of the proximal convoluted 

 portion of one tubule, may penetrate for a longer or shorter distance 

 into the coil complex of another tubule, so that in sections the former 

 might readily be interpreted as belonging to the latter. Stoerk gives in 

 Fig. 13 of his article a portion of a section of a kidney showing nephritis 

 ha?morrhagica, certain tubules of which contained red blood corpuscles; 

 this enabled him to select the sections of M^alpighian corpuscle and 

 tuluiles belonging to one uriniferous tubule. The section reproduced 

 shows a characteristic relation of corpuscles and tubules cut, such as is, 

 however, not frequently met with, if I may judge from the sections 

 from which my reconstructions were made. The relations there shown 

 are more nearly approached in Fig. 22 and also in the sections from 

 which model A of Fig. 19 was made than in other series of sections used 

 in modelling the other older developmental stages presented. 



It is somewhat hazardous to attempt an estimate of the length of a 

 fully developed uriniferous tubule, without the possession of models 

 showing them in full development. Since, however, the proximal and 

 distal convoluted ])ortions of certain uriniferous tubules attain approxi- 

 mately their full development before the birth of the embryo (cat and 

 rabbit), and since the length of the loop of Henle of these tubules de- 

 pends on the width of the medulla, as they extend through or nearly 

 tlirough the medulla, an estimate of the length of a fully developed 

 tul)ule seems justifiable. The length of tubules must necessarily vary, 

 since the loop of Henle, which for the majority of tubules forms their 

 greatest part, must vary in length, since they terminate at different 



