322 



THE ANIMAL PARASITES OF MAN 



mature segments are longer than wide (6 to 7 mm. by 2 to 3 mm.), fairly 

 thick, are frequently of a reddish colour, and when cast off resemble 

 cucumber seeds. The genital pores lie symmetrically at the lateral 

 margins ; the roundish egg sacs, arising from the uterine reticulum, 

 contain eight to fifteen eggs embedded in a reddish cement substance 



(in life). The eggs are globu- 

 lar (43 fi to 50 fjb) ; the em- 

 -.rjH bryonal shell (embryophore) is 



/: thin, the oncosphere measures 



32 //, to 36 fju. Surrounding the 

 embryophore is an albumin- 

 ous coating, and outside this 

 the thin vitelline envelope 

 (fig. 218). 



Dipyiidium caninum is a 

 common intestinal parasite of 

 dogs, in which it grows larger 

 (Tcenia cucumerina, Bloch) 

 than in cats (T. elliptica, 

 Batsch) ; it has, however, also 

 been found in jackals, as well 

 as in human beings, though 

 in the latter it is of compara- 

 tively rare occurrence (twenty- 

 four cases), and almost always 

 affects children, generally of 

 tender age. One-third of all 

 the cases in children were 

 sucklings, about a quarter of 

 all the cases recorded were 

 adults, and these occurred 

 throughout all Europe with 

 the exception of Spain and 

 Italy. 



The proglottids, which 

 leave the intestine spontane- 

 ously, are recognizable by the 

 naked eye on account of their 



FIG. 221. Larva (cysticercoid) of Dipylidium 

 caninum, consisting of body and tail. The latter 

 is solid and bears on it the embryonal spines. The 

 bladder, which was only slightly developed, has 

 disappeared, and the fore-part of the body bearing 

 the rostellum is now seen invaginated into the 

 hind portion. The hooklets are shown in front 

 of the excretory system which has now developed. 

 At a further stage the tail drops off; the head now 

 evaginates, but is still enclosed in a double-walled 

 sac formed by the prolongation upwards on each 

 side of the topmost parts of the body shown in 

 the figure. Cf. fig. 220, 6. Enlarged. (After 

 Grassi and Rovelli.) 



form and reddish colour, as 



well as their two genital pores. As a rule, the presence of this parasite 

 sets up no marked symptom in the patient. 



The corresponding larval form (cysticercoid) lives in the louse 

 of the dog (Trichodectes canis), a fact that was first established by 

 Melnikow and Leuckart ; according to Grassi and Rovelli, as well 



