46 LECTURE IV. 



having heard this description of a free and independent being, whose 

 tissues ai-e chemically proved to be of an animal nature, imbibing 

 nourishment without vascular connection with the cavity containing 

 it, and reproducing its kind, how is an animal to be defined if this be 

 not one ? The answer that the acephalocyst has no mouth may, 

 perhaps, not be regarded as satisfactory. Definitions apart, our 

 business is to discover to what organic thing the acephalocyst is 

 most analogous. 



The primitive forms of all tissues are free cells, which grow by 

 imbibition, and which develope their like from their nucleus of 

 hyaline. All the animal tissues result from transformations of these 

 cells. It is to such cells that the acephalocyst bears the closest 

 analogies in physical, chemical, and vital properties. When the 

 Infusorial Monads are compared to such cells, and man's frame is 

 said, by a figure of speech, to be made up of such monads, the 

 analogy is overstrained, because no mere organic cell has its mouth, 

 its stomachs, its testes, and ovaria. So also it appears to me that 

 the analogy has been equally overstrained, which makes the acepha- 

 locyst a kind of monad, or analogous species of animal. We may, 

 with some truth, say that the human body is primarily composed or 

 built up of acephalocysts ; microscopical, indeed, and which, under 

 natural and healthy conditions, are metamorphosed into cartilage, 

 bone, nerve, muscular fibre, &c. When, instead of such change, the 

 organic cells grow to dimensions which make them recognisable to 

 the naked eye, such development of acephalocysts, as they are then 

 called, is commonly connected in the human subject with a lowering 

 of the controlling vital energies, which, at some of the weaker points 

 of the frame, seem unable to direct the metamorphosis of the 

 primitive cells along the right road to the tissues they were destined 

 to form, but permits them to retain, as it were, their embryo con- 

 dition, and to grow by the imbibition of the surrounding fluid, and 

 thus become the means of injuriously affecting or destroying the 

 tissues which they should have supported and repaired. 



I next proceed to consider the internal parasites, Avhich present 

 the characters assigned by Rudolphi to his Cystic Entozoa. 



Tlie name Echinococcus is given to a cyst resembling the acepha- 

 locyst, when, in addition to the sero-albuminous fluid, it contains a 

 number of microscopic organised beings, floating, or freely swimming 

 in it, or adhering by special prehensile organs to the internal surface 

 of the cyst. They are quite independent of the acephalocyst, which 

 merely forms their place of abode ; and to them I would limit the 

 generic name Echinococcus, which indicates one^ of their organic 

 characteristics, namely, a coronet or cylinder of spines, which 



