CLASSIFICATION OP THE ANIMAL KINGDOM. 53 



the surface." The instruments of sensation in the Acahphce are the tentaeula 

 and suckers appended to the body. No nervous system has been discovered 

 with any accuracy, if at all, in even the largest Medusae, and the organs 

 of reproduction seem to be little better understood, though several authors 

 have described the position of ovaria in various parts of the body. 



We now come to the last family of acrite animals, the Sterelmintha, 

 or Parenchymatous Entozoa, creatures which are nourished, as their name 

 implies, in the interior of other animals. The simplest of this class are 

 the Cystiform Sterelmintha, or Hydatids, one of which, the Ccenurus cerebralis, 

 abundant in the brains of sheep, and met with in other ruminants, is 

 shaped like a bladder, with numerous mouths furnished with hooks appended 

 to it; others have only one mouth, as the Cysticercus crassicollis. The 

 mode of reproduction of these curious creatures resembles that of some of 

 the Polyjastrica before mentioned, as the young are formed by gemmules 

 growing in the inside of the stomach, which in course of time become 

 detached, and burst through the body of their parent. Among the most 

 interesting of this last tribe are the Taenia, or Tape-worms, several of 

 which infest the human body, and attain to the prodigious length of 

 twenty or thirty feet. The body of the commonest consists of a series 

 of linear segments united together, and increasing in size towards the middle; 

 and each of these segments may be regarded as a distinct animal, for 

 every one of them is found to possess a complete generative apparatus, 

 the ovaria occupying the centre of each joint. The head is of a very 

 singular shape, and is provided with a mouth in the centre beset round 

 with spines. The alimentary canal consists of two tubes, which extend 

 through the whole length of the body, having cross canals in each segment, 

 which unite them. 



The next in order are much more highly organized animals; they are 

 called Distoma, or Flukes, and are commonly found in the liver and 

 biliary ducts of sheep. These little parasites excel all preceding ones in 

 the development of their generative system, which is very voluminous; 

 they are hermaphrodite animals, and their structure is very peculiar. 



The Planarice, which seem not altogether properly to belong to this 

 class, are next described. They cannot be classed as Entozoa, as they 

 inhabit ponds and stagnant waters, and in some respects they are decidedly 

 inferior to the animals placed below them, which have been just described. 

 They resemble gelatine in appearance, and can be multiplied by mechanical 

 division. Their mouths are usually placed on the ventral aspect of the 

 body. Their digestive apparatus resembles that of the Distoma, and the 

 stomach has only one orifice, in this respect therefore being inferior to 

 some Polygastrica. These animals are also hermaphrodite, like the last. 



One more type of this class is mentioned in the Professor's book, the 



VOL. VII. i 



