488 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



up a single mass, which lies well forwards, and is 

 composed of a number of blind tubes ; the whole 

 ovary is not very large. The yolk glands occupy the 

 sides of the body, extend farther forwards than the 

 ovary, and reach to quite the hinder end ; they are 

 racemose in character, each lobule being made up of 

 a number of small vesicles, the ducts from which open 

 into a large longitudinal duct, of which there is one 

 on either side of the body. Just below the level of 

 the ovary each of these gives off a transverse duct, 

 which opens into a common median reservoir; the 

 duct from this, after a somewhat irregular course, 

 during which it gives off the fine duct of Laurer and 

 Stieda which opens by a very minute pore on the 

 dorsal surface of the body, opens into the genital 

 sinus ; the terminal part of the duct serves as a 

 vagina. At the commencement of its course, where 

 it unites with the short oviduct, it is surrounded by a 

 complex of glands, the so-called shell glands, which 

 are so called from their secretion serving to form a 

 shell for the ova. 



In the round worms (JVeniatolielinintlies) the 

 sexes are nearly always separate, and the generative 

 products are developed in special tubes, which in the 

 female are, however, of considerable length. Owing 

 to their length, the female tubes are in most cases 

 coiled, but this is the only character which presents 

 any complexity ; the blind end of the tube serves as 

 the seat of production of the egg cells, and the re- 

 mainder has the function of an uterus, or of a vagina. 

 Here, again, we find that while the blind ovarian 

 portions of the tubes are double., the efferent portion 

 (vagina) has undergone fusion, and the generative 

 orifice is therefore single and median. The male 

 tubes have essentially the same structure, and are 

 only less complicated in character ; the blind end 

 of each tube is the seat of development of the 



