BY VERA IRWIN-SMITH. 239 



even where the forking of the common trunk occurs in front of the vulva, and 

 the direction of all four uteri is at first anterior, or where the whole system is 

 directed backwards, behind the vulva. The latter arrangement, shown in Text- 

 fig. 13, is that most commonly found in immature specimens under 25 mm. in 

 length, though some young specimens as small as 18 mm. show the forward ex- 

 tension which is present in all the older individuals. 



The exact position of the most anterior loops of the uteri varies consider- 

 ably, and has no constant relation to the total body leng-th. Some specimens 

 less than 20 mm. long have been found with the anterior uteri reaching far for- 

 ward, beyond the base of the oesophagus, while in mature specimens between 34 

 and 43 mm. long, the anterior loops may be found either behind or in front of 

 the junction of oesophagus and intestine, the distance from the anterior ex- 

 tremity varying from 1.5 mm. (43 mm. specimen) and 2.6 mm. (34 mm. specimen) 

 to 7.8 mm. (40 mm. specimen). In the latter example (40 mm. specimen), 

 which is shown in Text-fig. 12, and of which the complete measurements are given 

 in the table (p. 243), the vulva is rather exceptionally far from the anterior 

 extremity, 11 mm. distant, where other individuals of the same length have it 

 9 mm. distant. 



The distance of the most posterior loops of the uteri from the posterior 

 extremity varies similarly, from 13.3 mm. in a 43 mm. specimen, to 4.1 mm. in 

 a 34 mm. specimen; and the receptacula seminis may be situated either in front 

 of the uterine loops or behind them (Text-fig. 17), at a distance of 11.9 to 5.2 

 mm. from the posterior end. In young specimens of 20 to 25 mm. length, the 

 uteri are more closely packed than in the older individuals, and frequently do 

 not occupy more than 3 or 4 mm. of the total body length. In an immature 

 specimen IS mm. long, in which the anterior extension of the uteri is very pro- 

 nounced, the receptacula seminis are found only 2 mm. behind the level of the 

 vulva, and the uteri do not extend more than 1 mm. further back, so that the 

 whole genital system is grouped in the anterior half of the body. Even in the 

 more common arrangement among immature specimens, in which it lies entfrely 

 behind the vulva (Text-figs. 13, 14), the narrow, delicate, poorly developed uterine 

 tubes do not extend far posteriorly, usually terminating at a distance of 6 to 11 

 mm. from the tail. 



The dimensions of the various parts of the system vary quite as much as 

 their disposition, and measurements taken from a single specimen are of little 

 specific value. 



In many adult individuals the reservoir is sharply delimited, and much 

 dilated, being crammed with eggs, while the common trunk is also distended 

 with eggs, and a continuous row of eggs extends along the vestibule to the vulva 

 (Text-fig. 16). But in other adults of the same size, which have large uteri dis- 

 tended with eggs, the reservoir swelling is slighter and more gradual, its limits 

 less clearly defined, and the few eggs in it are gathered into a cluster towards 

 its middle; while no egg-s are present in the .vestibule, the walls of which are in 

 contact, and only a few isolated eggs occur in the common trunk. Some immature 

 specimens have the position of the reservoir marked only by a slight increase in 

 diameter in the otherwise uniform trunk, due to the presence of a single row of 

 eggs there, no other eggs being found till the uteri are reached (Text-fig. 14), 

 but in other specimens not more" than 18 mm. long, in which the uteri are only 

 .08 mm. wide, and contain only one or two rows of undeveloped eggs, the re- 

 servoir is already well defined, and has a greater diameter than in mature worms 

 of twice the size. The reservoir, therefore, appears to be simply a more or less 



