igos.j EXCRETORY ORGANS OF METAZOA. 555 



of these canals are closed, and each is lined by a cuticula. Four 

 types of these have been distinguished according to their form and 

 position of the nephridiopore (Jagerskiold, 1898). A more careful 

 description has been furnished by Goldschmidt (1906) for Ascaris 

 hiuibricoides, who found that the whole apparatus is composed of 

 but two cells, with a single nucleus for both main canals and one 

 for the anterior unpaired duct. Goldschmidt further considers 

 these canals to be simply for discharge, and that a peculiar solid 

 tissue of the lateral lines is the true secretory portion ; these gland- 

 ular masses are multinuclear and do not touch the wal,ls of the 

 canals, but fine pores appear to extend towards them from the 

 lumina of the canals. In his own words : " The excretory system 

 of Ascaris . . . consists of the excretory gland proper (analogous 

 to a kidney) that lies within the lateral lines, and of the discharge 

 duct (analogous to a ureter) that consists of two horseshoe-shaped 

 limbs composed of a single cell and of an unpaired terminal portion 

 represented by one cell." 



Little is known of the development of these canals. They lie 

 within the lateral lines, and Zur Strassen (1892) has shown that 

 the latter are mesoblastic. Conte (1902) found the excretory 

 apparatus to arise from a single mesoblast cell that becomes sec- 

 ondarily placed in the lateral line. 



12. GORDIACEA. 



For this group specific excretory organs are still unknown, 

 though it has received much study. Vejdovsky (1886, 1894) has 

 interpreted the peri-intestinal cavity as excretory, but this has no 

 opening to the exterior ; and he has suggested that the oviducts and 

 vasa deferentia are modified nephridia, — a conclusion drawn from 

 his idea that the Gordiacea are degenerate annelids, a standpoint 

 that has been combated by me (1903a). In late embryonic stages 

 he found a " braune Driise " opening into the intestine near the 

 mouth ; this is not found in the adult, unless the problematical supra- 

 intestinal orgon described by me for Paragorditis may be an ex- 

 cretory organ conveying fluids from the peri-intestinal space to the 

 intestine. It is probable that excretion must take place through 



