70 



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

 then dissolved from arouhd 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 the larva 

 resembles the Acari (Plate XVII, Pig. 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 feet 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 traustbl-med into another larva by a series of successive 

 moults (see Fig. 6). The body is elongate, larger. forward, and is divided into eighty 

 to ninety rings bordered behind by a series of fine spines. The digestive tube is 

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

 accessory hooks. Tlje larva is agamic, its genital organs being rudimentary and rep- 

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

 the sixth or seventh month the larva is completely developed, measures 6 to 8™"! long, 

 and is in the stage called Linguatula dentieulata. 



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

 there for some time. They eventually escape, but the precise 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. 

 Tbese larva? can acquire their full development only in the respiratory passages. Once 

 installed in the nasal cavities they develop into egg-bearing adults. The males wan- 

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

 sedentary, and ar-e never found in the ethmoidal cavities. After tlie death of the 

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

 themselves into the frontal sinuses. They are 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, Linguatula denticulata, 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 th&gland is destroyed and transformed into 

 a brown tumor, in the middle of which are the Linguatulm. 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 false membranes, which indicate a recent departure or a de- 



