100 ANIMAL PHYSIOLOGY. [LESSON 29. 



498. They vary from the size of a pea to that of a child's head ; 

 in the larger ones the wall of the cyst has a laminated texture. 

 They are of a pearly whiteness, without fibrous structure, elastic, 

 spurting out their fluid when punctured. 



499. So far as known, there are two species of this animal ; one 

 the Acephalocystis JEndogena, or the " pill-box Hydatid " of Hunter, 

 most commonly found in man ; and the Acephalocystis Exogena, 

 found in the Ox, and other domestic animals. All these animals 

 multiply by fissiparous division, precisely like the multiplication of 

 the cells of plants, to which they appear to be most nearly allied. 

 In the first named species, this process takes place from the internal 

 surface of the parent cyst, and in the last, from the external surface 

 hence their specific names, respectively. 



500. Another parasite, closely allied to the above, the C&nurus 

 Cerebralis, is found in the substance of the brain of Sheep, Calves, 

 Pigs, Rabbits, and even Dogs, and produces a disease called (in 

 England) the " gid," or " mad staggers." 



501. In this disease, the animal affected by it appears to be 

 " giddy," and staggers with the head down to the ground, or butting 



FIG ill against extraneous substances in a state of apparent 



unconsciousness. A figure of this parasite is 

 given (Fig. 171). 



502. The Coanurus is one of the most simply 

 organized animals, consisting of a large bag (c) 

 always filled with water, at the end of a long neck 

 (5), the summit of which is provided with suctorial 

 mouths (a), adapted alike to adhesion to the tis- 

 sues by which it may be surrounded, and for the 

 procuration of nutriment. They are frequently 

 found provided with many heads, which can be 

 retracted within, or protruded without the com- 



Comurus cerebral*. mon cygt 



503. This Hydatid form is by no means uncommon as a parasite 

 in the animal kingdom and in man, and, wherever found, they in- 

 variably produce distressing, if not fatal disease. They have no sex, 

 and appear to propagate most abundantly by the mere act of spon- 

 taneous division, such as is common to plants, and to the Acephalo- 

 cysts. 



Of course, there can be no cure for the Coenurus, and the best 

 that can be done is, to terminate the animal's suffering as soon as 

 the " gid " makes its appearance. After death, pass a saw round the 



