520 



THE ANIMAL PARASITES OF MAN 



eially in the cyclops serrulatus, Fischer, and diaptomus spinosus, Daday; and 

 since these are frequently found in stagnant waters, the occurrence of the 



parasite in geese and ducks is quite 

 natural. The crabs, which are often 

 difSeult to recognize, occasionally mi- 

 grate with the drinking-water into the 

 intestiaal canal of man; the cercocyst 

 inhabiting the crabs develops into hy- 

 menolepis lanceolata. 



I V 



r 



Fig. 46. — Htmeno- 

 LEPis Lanceolata, 

 Bi-ocH. Enlarged 

 about twentytimes. 



Fig. 47. — Head, 

 Greatly En- 

 larged. 



Fig. 48. — Proglottid of Htmenolepis. 

 This preparation I owe to the kindness of Pro- 

 fessor W. Miiller of Greifswald. 



The most familiar of the bothrioeephali is the 



Bothriocephalus latus, Bremser, 1819. 



This broad bothriocephalus, called also the pit-head, measures 5-9 meters 

 and is the longest tape-worm of man. The club-shaped head shows on its 

 lateral border on each side an elongated, slit-like pit. The individual pro- 

 glottides, 3,000 to 4,200 in number, are remarkably broad in proportion to 

 their length. A grayish-blue centerpiece of rosette-like form bordered by 

 two narrower bands is distinctly visible upon both surfaces. On the ventral 

 surface are the male sexual opening and the mouth of the vagina. The 

 mature ova are ovoid in form and surrounded by a brownish shell with a lid. 

 The ova are rarely found in the last mature segments of the chain. Large 

 numbers of proglottides are often expelled at once. They are voided with the 

 feces, having been previously discharged from the uterus. If the ova reach 

 the water, ciliated embryos develop within them, which slip from the shell 

 of the ova and float for some time in the water. The ciliated covering perhaps 

 seeks the intermediary host, which, as we learn from Braun's brilliant investi- 

 gations, was found to be the pike (esox lucius), the burbot (lota vulgaris), 

 the perch (perca fluviatilis), the trutta vulgaris and lacustris, the thymallus 

 vulgaris, and the onchorhynchus Perryi. It is still undecided whether this 

 list exhausts the number of intermediate hosts. 



The young of the bothriocephalus, plerocercoides, dwell encapsulated in 

 various parts of the intestines and of the musculature, and usually in large 

 numbers. 



Bothrioeephali have been cultivated by feeding experiments with pleT0-_ 

 cercoides in the dog, the cat, and also in man. 



The transmission of the parasite undoubtedly occurs by means of fish. It 

 takes place frequently in infected districts where fish are eaten raw, half 

 cooked, or after any other mode of preparation which does not effect a destruc- 

 tion of the ova. It is remarkable that living ova have been demonstrated 

 even in fish that were frozen stiff. 



