STERELMINTIIA. 81 



thousandth part of the diameter of a hair ; and Clifton Wintring- 

 ham, in order that our ideas concerning them should be as perfect 

 as possible, recorded his estimate of the weight of one of these 

 animalcules, which he supposed might be about the hundred and 

 forty thousand millionth part of a grain !* Notwithstanding their 

 inconceivable minuteness, however, the Zoosperms have each a 

 definite and symmetrical figure, which is peculiar to their species, 

 so that those taken from different animals may be recognized by 

 their outward form. In quadrupeds they have generally the ap- 

 pearance of minute tadpoles, with flattened globular bodies, termi- 

 nated by long tails of extreme tenuity ; but, in fishes and inverte- 

 brate animals, they are often without tails, sole-shaped, or even 

 globular. Nothing of course is known concerning the internal 

 organization of these living atoms. 



(110.) The Cystiform Sterelmintha, which are generally known 

 by the name of Hydatids, are the simplest in structure ; and with 

 these, therefore, we shall commence our enquiry into the economy 

 of these creatures. The Ccenurus cerebralis, (Jig. 33,) one of 



Fig. 33. 



the most common, is met with in the brains of sheep, and is the 

 cause of a mortal disease but too well known to the farmer ; it is 

 likewise occasionally met with in other ruminating quadrupeds, 

 and, by partially destroying the substance of the brain, soon proves 

 fatal. This entozoon, represented in the figure of its usual size, 

 consists of a delicate transparent bladder, the walls of which, 



* De Blainville, (H. M. D.) Manuel d'Actinologie. Paris, 1834. 8vo. 



G 



