202 TAPEWOEMS OF HARES AND BABBITS STILES. VOL.XIX. 



0.560 to 1.800 mm. ; head, 0.352 to 0.512 mm. long by 0.320 to 0.480 mm. 

 broad; rostellum, 0.176 to 0.240 mm. long by 0.112 to 0.160 mm. broad; 

 number of hooks on rostellum, 100 to 122; on some fresh, specimens as 

 few as 90 hooks were counted; size of hooks on rostellum, 18 to 24 // 

 long. 



As in the case of the unarmed heads mentioned above, there was a 

 general though not absolute agreement between the size of the scolex 

 and the length of the parasite, and there is no question in my mind 

 that the head of a tapeworm is subject to increase in size after entering 

 its final host; numerous observations upon young specimens of tape- 

 worms from sheep support this view. 



In none of these armed specimens was there the slightest trace of 

 segmentation. In many cases the armature was not complete either 

 upon the suckers 1 or upon the rostellum, but in all cases some hooks 

 were found, and the rostellam was always visible. 



Taking all these observations into consideration. I am forced to the 

 conclusion that the unarmed forms and the armed forms represent the 

 young stages of two different species. The unarmed forms I am in- 

 clined to bring into connection with C. variabilis, p. 192, while the close 

 agreement between the rostellum of this young stage with that of D. 

 salmoni, the agreement in the size of its hooks, the agreement in the 

 general arrangement of the hooks on the suckers, the fact of their 

 presence in the same host species, and finally the fact that one of the 

 adult specimens ofD.salmoni (No. 1124,U.S.N.M.) was found in the same 

 locality in which these forms were found, all lead me to the conclusion 

 that the young armed stage here described represents the young of 

 Davainea salmoni. Experimental demonstration of this view is, how- 

 ever, lacking. In several specimens studied alive, the cysticercoids 

 were surrounded by a membrane (Plate XXV, figs. 4,8,10), which, 

 however, became entirely lost upon being subjected to technique. 



Armed larval forms distributed as follows. America: Collections 

 Bureau of Animal Industry; U.S.N.M. ; Harvard; Leidy; Hassall; 

 Stiles. Europe: British Museum ; E. Blanchard ; liailliet ; Moniez; 

 Zschokke; Parona; Berlin Museum; Leuckart; von Linstow: Looss; 

 Halle Zoological Institute; F. E. Schulze. Specimens will also be sent 

 to Neumann, Stossich, Monticelli, and Max Braun. 



Diagnosis. Davainea salmoni, Stiles, 1895. Strobila attains 86 mm. 

 or more in length and 3 mm. in breadth, and contains about 450 seg- 

 ments which vary in form from nearly rectangular to infundibuliform 

 according to contraction, most segments being much broader than long, 

 the distal 15 to 20 segments becoming longer and narrower, nearly 

 square, 1.8 by 1.4 mm. Head 0.6 to 0.736 mm. broad by 0.38 to 0.448 

 mm. long. Rostellum retractile, 0.1 to 0.14 mm. in diameter, armed 



'The number of hooks given for the suckers (150 to 200 at least) in Notes sur les 

 Parasites 31 is very greatly underestimated. It is utterly impossible to count them, 

 but I should now estimate the number about 750 for each sucker. 



