114 JESSE LE ROY CONEL 



duct. Again, the first Malpighian body of the mesonephi-os 

 may be located at the anterior end of the duct, and its tubule 

 may be widened to form the beginning of the duct, or the latter 

 may extend slightly anterior to the Malpighian body, in which 

 case the tubule enters the duct at the side. Two or three Mal- 

 pighian bodies may be crowded close together around the anterior 

 end of the duct, but their tubules always enter the lumen of the 

 duct separately and in consecutive order (fig. 54, a drawing of 

 the anterior ends of the ducts of Bdellostoma 4). On the left 

 side Malpighian bodies 1, 2, and 3 are very close together. 

 The first two are in one somite, 3 occupying the next segment. 

 When the Malpighian bodies are thus crowded together at the 

 anterior end of the duct, the arteries which supply them arise 

 from the aorta at successive points close to the posterior end of 

 the pronephros, a condition which suggests that these Malpigh- 

 ian bodies have been pushed back from a more anterior loca- 

 tion. For example, the point of origin of the artery which sup- 

 plies the first Malpighian body of the right duct of Bdellostoma 

 no. 15 is 3.5 mm. anterior to the Malpighian* body, and the latter 

 is only 5 mm. posterior to the caudal end of the pronephros. 



Except where the Malpighian bodies are occasionally crowded 

 together at the anterior end of the duct, there is but one in each 

 somite to somite 60-65. The ducts usually begin in somite 

 33-35, and the body cavity extends to somite 75-79, hence the 

 posterior third of the ducts have no Malpighian bodies. Price 

 learned that in embryos excretory tubules are present in the 

 most posterior somites, but they later degenerate in the last 19 

 or 20 segments. The most posterior Malpighian bodies in the 

 adult show signs of degeneration. They are small, often not 

 visible to the unaided eye, frequently in a shriveled condition, 

 and parts of them may be lacking ; for example, in one case the 

 tubule only is "present. This degeneration is of unequal extent 

 in different animals and on both sides of the same animal. 



Except an occasional one at the anterior end, all the Malpigh- 

 ian bodies lie along the median side of the duct. There is no 

 regularity in the orientation of the bodies with reference to the 

 somites; they may be located at either anterior or posterior side 



