ENTOZOA. 169 



having been accomplished, the hooks and tail drop off, and each larva passes 

 into the pupal afterward to assume the sexual form. 



In Bilharzia the eggs are of an elliptical shape. They develop minute 

 ciliated planulue. Their subsequent development has not been investigated. 



GESTODA (Tapeworms), Eudolphi. Composed of animals joined generally 

 for a long time to the nurse larva elongate and multiarticulate. Larva 

 (head) furnished with two to four pits or suctorial mouths commonly armed 

 with hooks; mature joints destitute of external organs, bringing forth em- 

 bryos armed with booklets ; alimentary canal none. 



Tsenia (Slender tapeworm.) Head subglobose or quadrangular ; suckers 

 four, rarely six ; muscular, orbicular, opposite, symmetrical, strongly contrac- 

 tile. Proboscis imperforate, retractile and inverted in scolex, but in mature 

 form protrusile. Armed with a simple double or multiple crown of hooks. 

 Body for the most part plane, white, depressed, bilateral, or triangular, strobile 

 articulate. Mature segments hermaphroditic, separating successively. Each 

 segment (called proglottis) resembles a Trematode. Water vascular system 

 transparent. Genital pores lateral, for the most part alternate. Male pore 

 larger and anterior, the female smaller and posterior. Genital organs per- 

 fect. Embryo small, active, and armed with little hooks; in those which go 

 through the ' cysticercus' form, oval, very small, ciliated, yellowish ; in other 

 larger, smoother and more transparent. (Klichenmeister.) 



T.solium (Hooked tapeworm), Linn. Head about the size of a pin-cap, 

 globular, but produced in front to form a short conical proboscis armed with 

 double row of hooks, from twenty to twenty-eight in each circular row; head 

 furnished with four sucking disks, and succeeded by a very narrow neck 

 nearly half an inch in length, the latter being continued into the anterior 

 portion of body, in which traces of segmentation at first appear in the form 

 of fine transverse lines, which gradually becoming more and more widely sep- 

 arated, leave brief interspaces. The earliest formed joints are narrow ; the 

 proglottides commence at about the 450th segment, the total number of joints 

 in a worm ten feet long being 800. The integument contains a number of 

 calcareous particles scattered through it, as well as a small quantity of 

 chitine. 



A longitudinal canal extends laterally along- both margins of individual. 

 They are in reality not continuous, but the canal of each segment is in a 

 degree complete. It pertains to a water vascular system. An opening sit- 

 uated at the side constitutes the sexual aperture ; the orifice is very distinct, 

 and pierces a prominent papilla. The pore is placed sometimes on one side, 

 sometimes on the other. In the centre of the projection is a small opening 

 in which is found a perforate intromittent organ (spiculum), which is in con- 

 nection with a tortuous vas dcferens. The testicle is placed toward the mid- 

 dle of the segment. Behind the male orifice, and frequently confounded with 

 it, is the opening of the female organs. The vagina passes parallel to the 



