IV. NEMERTINA 



255 



cellulose of T. solium, found in man, more frequent and of more important e i- 

 the cysticercus of Tcenia cchinococcus (fig. 232), which lives as an adult in the 

 dog, and is easily overlooked on account of its size. It is at most inch long 

 and consists of a scolex and three or four proglottids. When the eggs are taken 

 into the human stomach, as may easily happen by stroking and kissing infected 

 dogs, the embryos are set free and wander into liver, lungs, brain, or other organs 

 and produce here tumors which, in the case of the liver, may weigh ten or even 

 thirty pounds. This extraordinary size is explained by the formation of 

 daughter bladders (echinococcus) described above. 



FIG. 234. Heads and proglottids of three tapeworms of man. Left, Ta-nia sagi- 

 nala; middle, T. solium; right, Bothriocephalus latus, flat and side view of head. The 

 heads enlarged about six times, the proglottids about ii (after Leuckart, Braun, 

 and Schauinsland). 



Common Tee-nice of domestic animals are in the horse Anoplocephala plicata 

 (4 to 30 inches), A. perfoliata (\ to 3 inches), A. mamillana (J to 2 inches); 

 in ruminants, Moniezia,-* in the dog, T cent a marginata* (cysticercus in sheep 

 and swine), T. serrata* (cysticercus in rabbits), T. echinococcus (above), T. 

 ccenurus (cysticercus in brain of sheep, causing the disease called 'staggers'), 

 Dipylidium cucumerina* (most common, larva in the flea and dog-louse); in the 

 cat, Tcenia crassicollis* (cysticercus in mice). Several species occur in domestic 

 birds, one (Drepanidotcenia infundibuliformis*), causing epidemics among 

 chickens. Others in ducks and geese. 



Class IV. Nemertini. 



Most nemerteans are of appreciable size, some reaching a length of a 

 yard or more (Linens longissimus 90 feet !), and yet they are so contractile 

 that our Cerebratulus lacteus, which can extend itself to fifteen feet, can 

 retract to two. Nemerteans are rare in fresh water or moist earth, but 

 are most abundant in the sea, where they burrow through the mud or lie 

 rolled up beneath stones. Many are noticeable for their bright colors. 

 Their systematic position is a problem. 



