6o8 



CESTOIDEA 



Uterus becomes divided into ovarium follicles, or entirely atro- 

 phied, and the eggs are set free into the parenchyma. Eggs with 

 thin transparent shells, with or without appendages. 

 Genera.' — (i) Dipylidium ; (2) Hymenolepis. 



Dipylidium R. Leuckart, 1863. 



Befinllicn.— Dipylidiinse of medium or small size, with retractile 

 rostellum armed with several rings of alternating hooks, which 

 have a broad basis. Genitalia duplicated, with pores on each side 

 of a proglottis. Eggs with a double shell. 



Dipylidium caninum Linnaeus, 1758. 



Synonyms.- — TcEnia canina Leuckart, 1758; Monilijofmis Pallas, 

 1781; T. cummerina Blochmann, 1782; T. elliptica Batsch, 1786; 

 Dipylidium cucvtmerinum Leuckart, 1863. 



Dipylidium is frequently found in the dog and the cat, which are 

 its proper hosts ; in man it is only an accidental and rare parasite, 

 having been first found by Dubois, a pupil of Linnaeus, in 1751. 

 Melnikow showed that the scolex was to be found in the dog-louse 

 [Trichodedes canis) and in that of the cat {T. subrostratus), as well 

 as in the dog- flea {Ctenocephalus canis Curtis), the cat-flea {C. felinis 

 Boyche), and in that of man (P. irritans), but how the infection 



reaches man is not definitely 

 proved. Recently Blanchard 

 has summarized sixty cases in 

 man up to the year 1907, most 

 of which occur among young 

 children. 



Morphologyo — It measures 

 15 to 35 and even to 40 centi- 

 metres in length, and the seg- 

 ments are from 1-5 to 3 milli- 

 metres in breadth. 



The scolex has the typical 

 LiG. 251. — Dipylidnim canunvni rostellum, with three to four 

 Nest of Eggs. (X 250.) rings of hooks, diminishing in 



{From a photograph by J. J. Bell.) size from the first circle, where 



they are 12 to 15 to the last, 

 where they are only 5 to 6 /.e in length, and four suckers, which 

 are unarmed. 



The genitalia are double, with spores on each side. The eggs are 

 round, from 43 to 50 in diameter, with a thm shell. 



Life-History. — The ripe proglottides by their own movement pass 

 through the host's anus, and get into the fur, where the eggs infect 

 the dog and cat louse, or flea, in which they develop ii>to cysti- 

 cerco'ds {Cryptocystis trichodectis Villot, 1882). 



The dog bites the louse or flea, and infects itself, and may pass 

 on the cysticercoids to man by licking. The cat licks its fur, and 

 gets infected in that manner. 



