96 THE KIDNEYS, BY C. LUDWIG. 



tical to the medullary portions of the kidney until means 

 have been discovered rendering it more easy than at present to 

 isolate the tubuli uriniferi, and to obtain them in a less broken 

 condition. 



From the statements that have been made upon the anatomy of the 

 tubuli uriniferi in other vertebrate classes the following excerpts may 

 be made. 



The diagrammatic outline (fig. 149 D) is taken from the kidney of 

 the Pigeon, and the remarkable agreement it presents with the urinary 

 canals of the Mammal is deserving of notice. The several sub- 

 divisions of the tube distinguishable in the latter are seen to recur 

 there, and the epithelial covering preserves the same features in both. 

 As far as our present knowledge goes it would appear that the tubuli 

 uriniferi in all Birds resemble those of the Pigeon. 



Fig. 149 c represents the course of the urinary tubules in the 

 kidney of Testudo. We see here the capsule with its neck (i), the 

 dilated tortuous portion (n), the narrowed portion with which this is 

 continuous (in), and lastly the dilatation (v), immediately preceding 

 the formation of the collecting tube. The only differences existing 

 between this and the type found in Mammals are that the tortuous 

 portion of the tube is not smooth in Reptiles, but presents a nodu- 

 lated surface, and that the constricted portion lying between it and 

 the intermediary portion is of a different shape than the loop of 

 Mammals. The epithelium in the neck of the capsule in the Tortoise 

 is but little elevated, whilst it is high and sometimes pigmented in 

 the tortuous portion, and flat and transparent again in the narrowed 

 portion. 



Fig. 149 B shows the course pursued by the tubuli uriniferi in the 

 Frog. The elongated capsule is continuous by its protracted neck ([) 

 with the tortuous tube (n). This becomes attenuated at in, and, again 

 undergoing gradual dilatation, forms a second very tortuous portion (v), 

 which discharges its contents into the collecting tube. The wall of 

 the capsule is invested by a strong layer of connective tissue, and the 

 epithelium lining it is low, clear, and frequently ciliated. In segment 

 ii the epithelium is composed of tall polygonal cells, in in the cells 

 are transparent and low, and lastly, in the segment analogous to the 

 intermediary portion they are tall and cloudy. 



The urinary tubules of the Triton closely resemble those of the Frog 

 in their structure and course. 



Fig. 149 A is a diagram representing the urinary tubules of the 





