ENTOZOA. 65 



occasionally discharged."* The echinococci from a small musk- 

 deer ( Tragulus) closely resemble those of the hog. Each tooth or 

 spine presents an elongated triangular form, a small process extending 

 from the middle of its outer margin, probably for the attachment of the 

 ' protractor fibres. 



The Echinococci of the human subject {Jig. 24.), which have been 

 accurately described by Professor Miiller in a case where 

 they were developed in the urinary bladder, and which 

 OA^^ have been carefully figured by Mr. Quekett in a case ob- 

 Echinococcus scrvcd by Mr. Curling, where they were developed in the 



magn.' livcr, present well developed suctorious cavities (b), external 

 to the circle of teeth (a), and thus closely resembling the head of a 

 Tienia, appended to a small cyst. 



The hydatid developed in the substance of the brain of sheep and 

 rabbits, called Ccenurus cerebralis, consists of a large cyst, with which 

 many heads, like those of the Tteniae, are in organic connection. 

 These can be retracted within, or protruded without, the common 

 cyst. 



Our present knowledge of the generation of the CcBnurus is limited 

 to one of the alternating modes, viz., the gemmation of the armed and 

 suctorious vei'miculi. The common or parent cyst is composed of two 

 layers of substance, — the external one fibrous, or striated, in diiferent 

 directions ; the internal of a delicate pulpy texture, locally thickened, 

 and studded with minute clear cells. The gemmation of the vermiculi 

 is not a process of continuous growth from the tunics of the parent cyst, 

 but commences from an independent cell, situated between the layers, 

 like the commencement of the bud from the hydra. Mi*. Goodsirf has 

 figured the progressive multiplication of cells from the primary one, 

 closely analogous to the mode of establishment of the germ-mass from 

 the primary-impregnated germ-cellin the ovum, until the cellular basis of 

 the vermicule is established : it then pushes out before it the external 

 fibrous layer of the mother-sac ; and the organisation of the head is 

 completed by the metamorphosis of the pre-developed cells. At this 

 point, however, the generation by gemmation is arrested ; the young 

 individual is not cast off like the young Echinococcus or Hydra ; its 

 base continues in organic connection with the parent stock, and thus 

 a compound animal, or aggregate of vermiculi results, analogous to the 

 compound polypes, or as regards the general form of the community, 

 to the Volvox globator. 



* LX. p. 118. l^L-. Erasmus Wilson has noticed a similar fact in the Echinococcus 

 hominis. LXI. p. 36. pi. 1. fig. 8. "Some of the granular contents of the animal 

 expelled through the aperture left by the torn peduncle." 



t LIII. p. 56.5. pi. xvi. 



F 



