70 



wliere they lie until eaten by some herbivorous animal. The shell is 

 then dissolved from around the embryo, and it bores through the walls 

 of the stomach or intestine into the mesenteric gland, liver, or lung, 

 where it encysts itself. In its first stage of active migration tlie larva 

 resembles the Acari (Plate XVII, Fig. 4). It has an ovoid body, flat- 

 tened on the ventral face, rounded on the dorsal. Its posterior extrem- 

 ity is narrowed and dentate. It is furnished with two pairs of articula- 

 ted, two-clawed feet, and at its anterior end by a perforating apparatus 

 formed of a median stylet and two re-curved hooks. Its length is 

 0.13'"'" ; its width 0.06'"'". 



Having arrived at the mesenteric glands, the liver, or the lungs, as the 

 case may be, the embryo loses its fieet and is transformed into an im- 

 movable pupa (Fig. 5), without segments, hooks, or hairs, measuring 

 0.250 to 0.300""" long, and 0.180'"'" in width. 



It emerges from this cyst transformed into another larva by a series of snccessive 

 monlts(seeFig. C). The body is elongate, larger forward, and is di-vided into eighty 

 to niuety rings bordered behind by a series of fiue spines. The digestive tube is 

 large, the mouth is elliptical, and surrounded with four characteristic hooks and with 

 accessory hooks. Tiie larva is agamic, its genital organs being riulinientary and rep- 

 resented only by a little granular mass in the posterior part of the body. Towards 

 the sixth or seventh mouth the larva is completely developed, measures G to y""" long, 

 and is in the stage called Linfjuatnla deniiculata. 



These larvae having escaped from the cyst, fall into the serous cavities and remain 

 there for some time. They eventually escape, but the i^recise method is unknown. 

 Next they are seen in the nasal cavities of dogs. Exceptionally, so it is said, they 

 are found in the nasal cavities of sheep and cattle, into which they have wandered. 

 These larvae can acquire their full development only in the respiratory passages. Once 

 installed in the nasal cavities they develop into egg-beariug adults. Tlie males wan- 

 der and can be found at- various points of the cavities, but the females are more 

 sedentary, and are never found in the ethmoidal cavities. After the death of the 

 host tliey may travel into the pharynx and larynx. They exceptionally introduce 

 themselves into the frontal sinuses. They arc generally found at the bottom of the 

 nasal chamber. 



As the adult stage is not usually found in sheep, and as its occurrence 

 is problematical in this country, the disease it causes will not be con- 

 sidered in this volume. 



Disease. — The young state, Linguatnla denficnlafa, found in cysts 

 within the glands, etc., are said to be particularly frequent in sheep in 

 Europe. Sheep in which the parasite affects the mesenteric glands are 

 generally less fat; their flesh is paler, and they are apparently predis 

 posed to anaemia. These glands show no evidences of the parasite at 

 first, but later they grow browner, smaller, and are crossed by galleries 

 filled with larvae. These cavities are separate at first, but finally com- 

 municate ; the substance of the gland is destroyed and transformed into 

 a brown tumor, in the middle of which are the Linguatukc. From these 

 the parasites often escape through openings with irregular borders; at 

 other times the surface is covered by dark, irregular spots, fibrinous de- 

 posits, and fiilse membranes, which indicate a recent departure or a de- 



