ANIMAL PARASITES. 137 



(Fig. 62) or fragments of the characteristically lamellated cyst walls. 

 The connective-tissue walls of the primary cysts may become fatty, or 

 caseous, or calcified. 



Sometimes the secondary vesicles project outward instead of inward, 

 forming a series of cysts outside of the primary one. This variety of de- 

 velopment is sometimes seen in man, but is more common in the domestic 

 animals. It is called Echinoccocus scolecipariens or exogena. 



Another variety of echinococcus, called E. multilocularis, is almost 

 always found in the liver, and appears to be the result of incomplete 

 and disturbed development of the embryos or cysts. It consists of a 

 congeries of irregular, usually small cysts (Fig. 372, page 609), surrounded 

 by broad and narrow bauds of connective tissue, and sometimes contain- 

 ing gelatinous fluid and scolices or booklets; but the latter structures- 

 are commonly absent or difficult of detection. The whole is often sur- 

 rounded by a dense connective-tissue capsule which may be calcified. 

 The entire mass often presents an alveolar structure and was formerly 

 regarded as a tumor alveolar cancer. The diagnosis may be established 

 by the discovery of the booklets or scolices, or fragments of the lamel- 

 lated cuticula. This form of the parasite is rare in America. 



There are four or five other species of tsenia, occurring rarely iii man. 



Tcenia, iiaiut. This species occurs in the form of small colonies, about 15 mm. in 

 length. The rostellum is surrounded by a single row of booklets. It has been seen 

 once in large numbers by Bilharz in the duodenum of a child which died of meningitis 

 in Cairo. Tcenid flacapunctata. a species about which little is known, is reported twice 

 in America as occurring in the intestine of young children. Twnia madagascarienzis, 

 also little known and rare, has been seen in two children in Madagascar. 



Tfenia cucumerina. This species occurs in colonies about 20 cm. long. The head 

 is very small and spheroidal, and has four rows of booklets. It is frequent in the 

 small intestines of dogs and cats. It occurs occasionally in man. Its scolex inhabits the 

 dog louse, and infection may occur in man by the transference of the lice or the embryos 

 of the parasite to the mouth, as the result of the filthy habit of kissing dogs and cats or 

 permitting the face to be licked by them. 



BotkriocepJialus latus. This, the largest of the human tapeworms, has very broad, 

 quadrangular proglottides. The head is ovoidal and about 2 mm. long and 1 mm. 

 broad. It has no proper sucking discs and no booklets, but by long grooves on either 

 side of the head the animal attaches itself to its host. The neck is long and filiform. 

 It occurs most frequently in Europe, particularly in the northern provinces. The eggs 

 undergo partial development in water, and are taken up by the pike and eel-pout, and 

 perhaps by other fresh-water fish, from the ingestion of whose flesh in an imperfectly 

 cooked condition the human infection occurs. Two other species of Bothriocephalus 

 have been described as of rare occurrence in man: B. cwdatus in Greenland and Iceland, 

 and B. cristatus. 



NEMATODA (Sound Worm*). 



These worms are in general cylindrical, elongated, usually pointed at 

 the ends, and sometimes filiform. The surface is sometimes smooth, 

 sometimes irregularly beset with hairs and papillae, or possesses longi- 

 tudinal elevated strife or transverse rings; but the body is not segmented. 

 There is a mouth at the anterior portion, and a ventral anus near the 



