182 



UNSEGMENTED " WORMS. 



the food consists chiefly of juices either from a living host 



or from putrefying organic matter, it is not surprising to 



find that the alimentary canal has usually but a narrow 



cavity. In some forms, e.g., Sphcerularia 



from the bee, it degenerates altogether. 



Normally it consists of three parts, a fore 



gut or oesophagus, lined by the inturned 



cuticle, a mid gut or mesenteron of endo- 



dermic origin, and a usually short hind gut 



or rectum, lined by the cuticle. When 



the external cuticle is shed, so is that of the 



fore gut and hind gut (cf. Crayfish). 



Body Cavity. 



A ccelome is developed and contains 

 a clear fluid, which probably discharges 

 some of the functions of the absent blood. 

 There are no amoeboid phagocytes. 



Excretory System. 



Imbedded in each lateral line there is a 

 long tube containing clear fluid, probably 

 drained from the surrounding tissues. The 

 two longitudinal tubes unite anteriorly, 

 and open in a ventral excretory pore near 

 the head. 



Reproductive System. 



The sexes are separate, except in Angio- 

 stomum which is hermaphrodite and self- 

 fertilising. In the male, the testis is 

 usually unpaired, a coiled tube gradually tureofaNematode 

 differentiating into vas deferens, seminal (Oxyuris). (After 

 vesicles, and ejaculatory duct. The genital GALEB.) 

 aperture is close to the anus, and beside it .'"-* Mouth; c.,cu- 



. .,, j f , . -i ticular ring ; #?., oeso- 



there are sensory papillae, and often spicules, phagus ; #., bulb con- 



and peculiar membranous folds of varied 



form \vhich constitute what is called the 



copulatory "bursa." The spermatozoa have 



not the typical form, and are sluggish. In the female, 



the ovary is a single or paired tube which passes grad- 



FIG. 59. Illus- 

 trating the struc- 



. te j, th ; t z ;' st |": 

 ?.<, vas deferens ;#! 



