TRANSACTIONS OP THE SECTIONS. S'j 



On the Structure and Development of the Cystic Entozoa. 

 By Harry D. S. Goodsir, M. W.S., and Conservator Mus.R.C.S. Edinburgh. 



In this very natural order of Entozoa the author places the Acephalocysts, which 

 were looked upon by Rudolphi and other helminthologists as being merely adven- 

 titious. 



Three verj' distinct forms of the genus Acephalocystis were described ; the specific 

 characters being derived from the structure of the germinal membrane (the membrane 

 from which the young originate), also from the mode of growth and structure of the 

 young Hydatids. 



In Acephalocystis simplex the membranes appear to be more or less inseparable, 

 transparent, and the young vesicles are very few in number. 



A. Monroi. — The germinal membrane of this species is divided, by means of a fibrous 

 tissue, into numerous compartments, each of which are occupied by a delicate trans- 

 parent vesicle filled with cellular substance, of which the cells or divisions are very 

 large. Each of these vesicles contains one or more small dark bodies — the young 

 Hydatids. 



J. 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 

 opake from the addition of young within them. 



A small transparent vesicle jutting out from the surface of the germinal membrane 

 is the first vestige of a young Hydatid, which speedily becomes opake in consequence 

 of young cells growing within it. This very soon separates, and then becomes what 

 the author terms a secondary Hydatid. The young cells which were seen growing 

 within it before its separation now also increase in size, and soon become parent cells, 

 but do not separate from the germinal membrane of their parent until she escapes 

 from the primitive Hydatid. Thus there are four generations, the primitive Hydatid 

 still containing the three generations to which she had given birth. 



If the primitive Hydatid is buried so deeply in the tissues of the infested being as 

 to prevent the escape of the secondary Hydatids with their two inclosed series of 

 young, decomposition ensues, upon which they speedily disappear. 



The author, after describing the very peculiar process of decomposition which takes 

 place in these animals under such circumstances, proceeded to describe two very 

 peculiar animals hitherto unobserved by naturalists, Astoma acephalocystis and Dis- 

 kostoma acephalocystis. They were considered to be connecting links between the 

 Acephalic and Cephalic Entozoa, and were the means of enabling the author to point 

 out many beautiful analogies which existed between the Entozoa and the other classes 

 of the animal kingdom. 



The structure and habits of the genera Csenurus and Cysticereus were then de- 

 Bcribed along with several new species, after which the author mentioned those 

 Entozoa of the higher orders, such as the Nematoid, Cestoid, &c., which inhabit cysts. 

 These species were not considered to belong to the Cystoid order of the class, but 

 were merely brought forward by the author as illustrative of several views which he 

 held relative to some points in the physiology of the Hydatids. He looked upon all 

 these Entozoa, as Trichina, Gymuorhynchus, &c., as still inclosed within one or more 

 of the membranes of the ovum, and that the inclosed animal received its nourishment 

 by means of a peculiar structure in the inclosing membrane. If a small portion of 

 the inclosing cyst of Gymnorhynchus horridiis be placed under the microscope it will 

 be found to consist of two membranes. The external consists of condensed cellular 

 texture, and is derived from the tissues of the infested being ; the internal membrane 

 consists entirely of absorbing cells, through which the contained animal procures its 

 nourishment. This is the general structure of all the cystoid Entozoa. Owing to the 

 presence of a foreign body, the tissues of the infested being in the neighbourhood of 

 the Entozoon throw out a quantity of lymph, which is always adding to the thickness 

 of the external membrane of the cyst, until at length it becomes so thickened and 

 hardened as to prevent the internal or absorbing membrane from procuring the re- 

 quisite means of nourishment for the support of the inclosed animal, which, if sta- 

 tionary, very shortly dies, as in Acephalocystis. Gymnorhynchus, however, which has 

 the power of motion, escapes this mode of extirpation, and when the cyst is examined, 

 it presents the following appearances : — The cyst all around the head of the animal 



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