Glass 3. Cestoda. 



153 



Very common in the Dog and Oat, rare in Man (cldldren). The prosoolex, 

 which has no bladder, lives in the Dog-louse {Trichodectes canis) ; according to 

 modem opinions, in the Dog-flea also. 



2. Bothriocephalus. The head with two long sucking grooves, without ti-ue 

 suckers and without hooks. The genital apertures are on the ventral side of the 

 proglottides, which are always short and wide. Uterus an unhranohed coiled 









Fig. 114. B. latus, part of the chain, natural size. — After Leuekart. 



canal. B. latus, the broad Tapewoiin of Man, common in the Russian Baltic 

 provinces, Finland, in "W. Switzerland, though extremely rare in England, 

 attains a length of 8 — 9 m. The proscolex lives in the flesh of the Pike, and 

 other fi-esh-water Pish. It is long, without a bladder (1 c/m. long). How the Fish 

 are infected is not known. The eggs of the Tapeworm develop in water, the newly 

 hatched larvse are provided with a covering of cilia and within them the six hooks 

 are found as usual. It has not, however, been found possible to infect the 

 Fish with the larvse, so that it is conceivable that the woiin lives first in another 

 host. On the other hand, it has been shown by experiment that the Pike- 

 proscolex transferred to the digestive tract of Man (and the Dog) develops into 

 B. latus. 



Class 4. Nemertinea {Bliyncii.oc(Eld) 



The Nemertines are, as a rule, elongate, often even ribbon-like, 

 animals of considerable ^ize. The skin is ciliated all over. At 

 the front end, on each side, is a slit-like, thickly-ciliate pit, a sense- 

 organ, which is also present in some Turbellarians ; dorsally and 

 anteriorly there is usually a number of small eyes. Quite at the 

 front end of the animal there is an opening leading into a deep eversible 

 blind sac, the proboscis. At the bottom of the sac, there is, in 

 many forms, a pointed stylet, which, when the proboscis is everted, 

 lies on its tip ; frequently a poison gland opens close beside 

 it. In others the spine is not present, but the proboscis is furnished 

 with numerous nettle-cells. When retracted (Fig. 115 (7) it is sur- 

 rounded by a muscular proboscis-sheath, and the space between 

 them is filled with fluid. The proboscis is everted by contractions of 



