152 EXCRETION. 



which recent observations have shown to be somewhat in- 

 tricate, it will be found most convenient to commence with 

 a description of the Malpighian bodies, and follow the course 

 of the tubes from these bodies to their connections with the 

 straight tubes of the pyramidal substance. 



Malpighian Bodies. These are ovoid or rounded termi- 

 nal dilatations of the convoluted tubes, of somewhat variable 

 size, measuring from -g-^- to yj-g- of an inch in diameter. They 

 are composed of a membrane continuous with that which 

 forms the convoluted tubes, of the same homogeneous char- 

 acter, but somewhat thicker, measuring about 2o ^ 0o of an 

 inch, while the membrane of the tubes is only about 4o ^ 00 

 of an inch in thickness. This sac sometimes called the 

 capsule of Miiller encloses a mass of convoluted blood- 

 vessels, and is lined with a layer of nucleated epithelial 

 cells. The question of the existence of epithelium within 

 the Malpighian body and the anatomical characters of the 

 cells have been the subject of considerable discussion. Bow- 

 man, in his original essay on the kidney, makes the state- 

 ment repeatedly that the vessels are bare within the capsule ; 

 and this has led some authors to suppose that he did not 

 recognize the presence here of any epithelium whatsoever. 

 This view favors the idea that the Malpighian bodies sepa- 

 rate only water from the blood, and that the cells lining the 

 convoluted tubes secrete the solid principles of the urine. 

 Bowman has never denied the existence of epithelium within 

 the capsule, but he regards it as of a different character from 

 that lining the tubes. His statement with regard to it is as 

 follows : " The epithelium is continued in many cases over 

 the whole inner surface of the capsule ; in other instances I 

 have found it impossible to detect the slightest appearance 

 of it over more than a third of the capsule." There can 

 be no doubt with regard to the constant presence of epithe- 

 lial cells within the capsule of the Malpighian bodies, particu- 

 larly since the researches of Gerlach, by whom they were 



1 BOWMAN, op. cit., p. 60. 



