424 FREDERIC T. LEWIS 



In the pig the tubules are more highly developed than in man. 

 They have been carefully studied by MacCallum, and are shown 

 in two published reconstructions which seem to reveal more than 

 is brought out in the accompanying text. Taken in connection 

 with two models now in the Harvard Laboratory, they indicate 

 that there is a pattern in the Wolffian tubule of the pig, quite 

 as definite and interesting as that of the metanephric or renal 

 tubule. Although a larger number of tubules should be modeled 

 to establish this conclusion and to show the range of variation, 

 the following interpretation of the somewhat laborious work 

 already done may be of value. A simple pattern for the human 

 tubules, and a more complex one for those of the pig, will be 

 presented, showing how both may be derived from a common 

 origin, one by simplification and the other by elaboration. 



Omitting from consideration the transformation of the pri- 

 mary vesicle, we may begin with the S-shaped stage which was 

 well described, and perhaps for the first time, by Kolliker in 

 1879. Referring to a rabbit embryo somewhat older than that 

 here shown in figure 1, he writes: 



"From the Wolffian duct there arises first a very slender tubule which 

 passes medially along the dorsal side of the Wolffian body, clear across 

 the organ; then, making a loop, it bends upon itself and retraces its 

 course to the lateral side; finally, after a third coil, it ends in the Mal- 

 pighian corpuscle, medially placed on the ventral side." He disposes 

 of the later stages as follows: "These three chief coils become compli- 

 cated by the formation, at the places where the bends occur, of acces- 

 sory coils in different planes, so that finally the course of a single tubule 

 becomes so complicated that it cannot be unravelled in sections." 



That the young tubules have the form of a letter S was further 

 established by Mihalkovics in 1885, from studies of the lizard, 

 duck, chick, and sheep. Beginning as a detached vesicle, the 

 tubule becomes cupped or crescentic, with the glomerulus develop- 

 ing within its concavity. It then takes the form of a 'ladle' or 

 'sickle,' as a short handle is marked off, joining the Wolffian duct. 

 This stage, as Mihalkovics found, gives place to the S. He con- 

 sidered that the distal limb of the S could be set apart as the 

 tubulus collectivus and that at the region of the distal bend it 

 became dilated and coiled, forming a tubulus secretorius, but 



