202 TAPEWORMS OF HABES AND BABBITS— STILES. 



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

 broad; vostelluiii, 0.17(1 to 0.240 min. long by 0.112 to (».1<»0 mm. l)road; 

 number of books on rosteUnm, 100 to 122; on some t'resb specimens as 

 few as 00 hooks were coimted; size of hooks on rostellum, 18 to 24 // 

 long. 



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

 general thougli 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 cavses the armature was not complete eitlier 

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

 were found, and the rostellum 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 ditterent species. The unarmed forms I am in- 

 clined to bring into connection with C variahilu^ j). 192, while the close 

 agreement between the rostellum of this young stage with tliat 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 linally the fact that one of the 

 adult specimens of D.mlmoni (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 forma distrlhutcd as folloivs. — America: Collections 

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

 Stiles, Europe: liritish Museum; II. Blanchard : Kailliet ; INIoniez; 

 Zsehokke; Parona; Berlin Museum; Leuckart; von Linstow; Looss; 

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

 to Xciimann, Stossich, Monticelli, and Max Braun. 



Diagnosis. — Darainca salmoni. Stiles, 1805. Strobila attains 86 mm. 

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

 ments which vary in form from Jicarly 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 0.73(5 mm. broad by 0.38 to 0.448 

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



' The number of books given for the stickers (150 to 200 at least) in Notes snr les 

 Parasitcis — 31 — is very j^reatly underestimated. It is utterly impossible to count them, 

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



