TYPE NEMATHELMINTHE8. 181 



those of the inner layer have a longitudinal course. The 

 body-wall encloses a well-marked coelom, not lined by a 

 special peritoneal epithelium, but which contains the repro- 

 ductive organs and is traversed by the retractor muscles of 

 the proboscis-sheath. 



The nervous system consists of a ganglionic mass (pg^) 

 lying within the proboscis-sheath which sends forward nerves 

 for the supply of the walls of the sheath and of the retractor 

 muscle of the proboscis. Posteriorly two lateral nerve-cords 

 extend backwards along the sides of the body, and in male 

 individuals are connected near the posterior extremity with a 

 ganglion lying beneath the reproductive ducts and from which 

 nerves pass to the genital apparatus. 



The system of lacunar canals which form a network in the 

 lower layers of the hypodermis is probably excretory in 

 function. The canals are found throughout the entire hypo- 

 dermis, both in the proboscis and in the body-wall, in the 

 latter there being indications of two larger lateral trunks. 

 From the point of junction of the proboscis with the body- 

 wall two muscular sacs, the lemnisci (I) , hang down into the 

 coelom. The cavity which they contain communicates with a 

 circular lacuna which surrounds the base of the proboscis 

 and with which the lacunae of the proboscis-hypodermis like- 

 wise communicate, this system of the proboscis-lacunse and 

 the lemnisci being shut off from the system of the body-wall 

 by a partition extending from the basement-membrane to the 

 cuticle. The lemnisci have been regarded as possible repre- 

 sentatives of a digestive tract, but it seems more probable 

 that they are reservoirs for the reception of the fluid con- 

 tained in the lacunae of the proboscis when it is driven from 

 them during invagination. 



The reproductive organs are much more complicated than 

 those of the Nematodes. The sexes are separate, the male 

 individuals being usually smaller than the females. The 

 ovaries are paired bodies enclosed within a muscular ligament 

 attached anteriorly to the base of the proboscis-sheath and 

 posteriorly to the reproductive duct. At an early stage of 

 their development, however, the ovaries split up into masses 

 which float about in the coelom together with large numbers 



