190 



PARASITES OF THE DOMESTIC ANIMALS 



2. Hymenolepis carioca. — The head is piriform with retractile 

 rostellum. It is unarmed. The segments number about 500, all much 

 wider than long; terminal segments measure 0.5-0.8 mm. The genital 

 pores are imilateral. The worm is very fragile and delicate. 



Length, 3-8 cm. (lM-3 1/8 inches). 

 The life history is unknown. 



3. Davainea tetragona (Twnia tetragona) . — The head (Fig. 104) is 

 small and tetragonal; rostellimi armed with a crown of 100 hooks. The 

 suckers are oval and armed with 8-10 circlets of small booklets. The 

 short neck is followed by short trapezoid segments, those terminal 



Fig. 103.— Choano- 

 taenia infundibulifor- 

 mis, scolex much con- 

 traoted, — • enlarged 

 (after Guberlet, in 

 ' ' Transactions of the 

 American Microscopi- 

 cal Society"). 



Fig. 104.— Scolex of 

 Davainea tetragona, — 

 enlarged (after Guber- 

 let, in "Transactions 

 of the American Mi- 

 croscopical Society".) 



ffi r^ 'fm tit , 



~^^' J 



' 1 '' 



Fig. 105. — Scolex of Davainea 

 echinobothrida, — enlarged (after 

 Guberlet, in "Transactions of the 

 American Microscopical Society".) 



generally longer than wide. Their length varies between 1-4 mm. The 

 genital pores are unilateral. 



The length varies between 1-25 cm. (3/8-10 inches). 



Investigations of Plana point to certain little snails {Helix carthu- 

 sianella and H. maculosa) as the probable larval hosts of this species. 



4. Davainea cesticillus {Tmnia cesticillus) . — The head is globular 

 and has a rostellum scarcely salient or depressed. It is armed with a 

 double crown of 400-500 booklets which are loosely attached. The 

 suckers are small and unarmed. There is no neck. The first segments 

 are short and much wider than the head; the last are about as long as 

 broad. The genital pores are irregularly alternate. 



Length, 1-4.5 cm. (3/8-1 3/4 inches). By some authors it is said to 

 attain a much greater length (10-13 cm.). 



