28 GUIDE TO THE STUDY 



vitelline gland. The sac-like uterus completely fills the ripe 

 proglottides. The eggs are large and transparent with two 

 envelopes, the inner double, and with two polar knotlike pro- 

 jections. The larval stages develop in various cereal-infesting 

 insects. (Fig. 9). 



Fig. 9. — Cysticercoids of Hymenolepis diminuta in body cavity of a beetle, 

 Tenebrio molitor. The three specimens lie adjacent to the large section of the 

 alimentary canal. 



Hymenolepis nana (von Siebold) is the dwarf tapeworm of 

 man, a species so minute and threadlike that it is usually over- 

 looked in macroscopic examinations. The adult worms measure 

 from 10 to 25 mm. (1 inch or less). The head has four suckers 

 and a simple crown of hooks. The general morphology is 

 similar to that of H. diminuta. The eggs can be distinguished 

 by the fact that there are filiform projections from the knobs 

 of the inner membrane. A striking exception to the usual rule 

 is the fact that these worms are able to complete their develop- 

 ment in a single host. 



Dipylidium caninum (Linn.) is one of the commonest tape- 

 worms of pet dogs and is also capable of developing in man. 

 It measures 10 to 40 cm. in length. The retractile rostellum 

 is provided with three or four rows of minute, thornlike, easily 

 detached hooks; the suckers are relatively large and ellipsoid. 

 The mature proglottides somewhat resemble cucumber seeds in 



