ANATOMY OF THE NEMATODES 367 



tubes pass out of the lateral lines, bend ventrally, and, in the median 

 ventral line, unite into a short vesicle formed by an ectodermal cell 

 the cavity of which is lined by a continuation of the cuticle of the 

 body which opens into the excretory pore (fig. 263, Exp.). Asym- 

 metry is occasioned through the excretory duct proceeding from the 

 ventral pore to the lateral line, and it here proceeds as (or takes up) 

 the left excretory canal, which anteriorly is a broader tube and runs 

 along the left lateral line ; shortly before its union with the excretory 

 duct it throws out a branch to the right towards the lateral line, 

 which, however, always remains weak, and runs posteriorly in the 

 right lateral line ; a few smaller branches in addition spring from 

 the left main stem. In other species the right branch is completely 

 suppressed ; the entire organ thus lies in the left lateral line, and 

 consists of the excretory duct, which occasionally opens quite in front 

 near the lips, as well as the excretory canal, which throws out a 

 number of lateral branches. 



This excretory vesicle is a single elongated or horse-shoe-shaped 

 cell, with a large nucleus and an intracellular tubular system, which is 

 connected with the excretory duct arising from the excretory pore on 

 the outer surface (fig. 326). The so-called ventral gland is the only ex- 

 cretory organ of marine Nematodes, and probably represents a primitive 

 form. Goldschmidt, who has investigated the excretory apparatus 

 of Ascaris hinibricoides, considers that the vessels running in the lateral 

 lines are only ducts to which belong a glandular system hitherto 

 overlooked or otherwise interpreted. This system also lies in the 

 lateral lines, and takes the form of two glandular tracts, forming 

 a syncytial tissue in which lie the ducts, one dorsal, one ventral. 

 In parts these tracts are connected by commissures, although their 

 junction with the excretory vessels cannot be clearly made out. These 

 statements, however, require confirmation. The author has further 

 found that the anterior ends of the lateral canals, directly before they 

 bend ventrally, anastomose with one another and give off anteriorly 

 a small blind process, which can be interpreted as a rudiment 

 of a canal coming from the head end, and as a matter of fact, 

 according to Golowin, such anterior excretory canals exist in a 

 number of genera. 



In a number of Nematodes (Cheiracanthus, Capillaria, Tricho- 

 cephalus, Trichinella, etc.), however, special excretory organs are 

 lacking ; possibly the cutaneous glands, which are in these species 

 generally powerfully developed, replace these organs. 



SEXUAL ORGANS. With the exception of a few species, the 

 Nematodes are sexually differentiated. 



(a) Female Sexual Organs. The sexual orifice (vulva), surrounded 

 by thick labia, is, as a rule, ventral and varies in position from near the 



