60 LECTURE IV. 



numerous and minute globules of a clear substance (c), analogous to 

 the " hyaline," whose remarkable properties in reproductive cells, Dr. 

 Bariy has demonstrated*, and from which the young acephalocysts 

 are developed. No contractile property, save that of ordinary elas- 

 ticity, has been observed in the coats of the acephalocyst ; no other 

 organisation than that above described ; no other function than that 

 of assimilation of the surrounding fluid by the general surface, and 

 the development of new cells from the nuclei of hyaline. It stands 

 on a still lower step in the series of organic structure than the Pro- 

 tococei of the vegetable kingdom ; for spontaneous fission has not been 

 observed in any acephalocyst ; and it ought, therefore, to be regarded 

 rather as an abnormal organic cell, than as a species of animal, even 

 of the simplest kind. 



Yet these productions have not escaped the ingenuity and dis- 

 criminative powers of the classifier. Of the numerous species, 

 nominal or real, which are to be found in the works of naturalists 

 and pathologists, I shall notice only a few: — 1st, the Acephalocystis 

 endogena of Kuhn, likewise called socialis, vel prolifera, by Cru- 

 veilhier : the " Pill-box Hydatid " of Hunter. It is the kind most 

 commonly developed in the human subject, and in which the fissi- 

 parous process takes place usually from the internal surface of the 

 parent cyst, the progeny being sometimes successively included : 

 and, 2dly, the Acephalocystis exogena of Kuhn, eremita vel steriliSy 

 of Cruveilhier, which developes its progeny generally from the ex- 

 ternal surface, and is found in the ox and other domestic animals. 



Mr. H. Goodsir, who has particularly studied the development of 

 the acephalocysts f, has described three species of the genus, the 

 specific characters being derived fi-om the structure of the membrane 

 from which they originate, and from the mode of growth and structure 

 of the young. 



In Acephalocystis simplex the membranes appear to be more or 

 less inseparable, transparent, and the young vesicles are very few in 

 number. 



In A. Monroi the ''germinal membrane" is divided by means of a 

 fibrous tissue, into numerous compartments, each of which is occupied 

 by a delicate transparent vesicle filled with cellular substance, of 

 which the cells or division are very large. Each of these vesicles 

 contains one or more small dark bodies — the young hydatids. 



In A. armatus the young arise from the germinal membrane of the 

 parent as very distinct small separate vesicles, which at first are quite 

 transparent, but soon become opaque from the addition of young 

 within them. 



* XXIX. t I^III. p. 563. 



