564 MR H - D - s - GOODSIR ON THE DEVELOPMENT, STRUCTURE, AND 



the former, inasmuch as the simple Hydatid was from its first appearance com- 

 posed of one cell only ; whereas, in this species, and particularly in this mode of 

 its growth, the cells, when first observed, contain a number of younger ones within 

 them, all of which afterwards become the separate and individual vesicle. (PL XV. 

 fig. 2, D G.) During this process, the tubular membrane increases in density 

 around and in the neighbourhood of the gemmules, owing to the increased number 

 of tubes necessary for their nourishment. It will be observed, that the young 

 original gemmule of this species resembles in its structure and functions, the adult 

 simple Acephalocyst. 



This species of Entozoon has two modes of propagation, viz., the one whicli 

 we have just described, for the purpose of increasing the size and extent of its 

 own individual group ; and another, for the purpose of extending the species to 

 uninfested portions of the infested animal. In the last, the mode of propagation 

 would appear to proceed in the following manner : The cells which have been 

 already described, in the preceding page, as occasionally seen detached from the 

 parent cell, and floating free in the gelatinous mass of the body of the parent 

 Hydatid, reach the healthy tissues which lie at some distance from the general 

 parasitic mass, (PL XV., fig. 2, C, D, and fig. 3, C), by some means which I have 

 been hitherto unable to detect. In general, they are no deeper than the subserous 

 tissue ; but when this has been already occupied, they are found much deeper, 

 where, as they increase in size, they tend always towards the surface of the in- 

 fested cavity, and at length burst from their confinement, adhering, at the same 

 time, to the bottom of their former, containing cellules by pedicles. (PL XV., fig. 2, 

 F.) In this manner a peculiar honey-comb appearance was produced, (PL XV., 

 fig. 5, C and D), by the breaking up of the tissues, which became much more appa- 

 rent when the Hydatids were removed from the affected surface. 



For the purpose of illustrating the series as completely as possible, I will 

 now describe the characters and mode of development of another form of Cys- 

 tic Entozoon. The Csenurus cerebralis is generally met with in the brain of 

 the sheep, and occasionally in the other ruminants. It consists of a vesicle 

 full of a transparent watery fluid. The cyst is double, the internal layer is 

 very delicate, Avhile the external is much stronger, acquiring additional strength 

 and thickness, in consequence of a great number of striae, which run through it 

 in all directions, and presenting, when seen under the microscope, all the charac- 

 ters, with the exception of the disks, of the tubular membrane of the new Ace- 

 pbalocyst, although not so strongly marked. Unlike the simple Hydatid, and 

 the parasite already described, the Csenurus possesses numerous heads (PL XVI., 

 fig. 13), arising at right angles from its external surface in groups, but apparently 

 without any regularity. Each head consists of a pedicle (PL XVI., fig. 13, C, H), 

 and head proper (PL XVI. fig. 3, A), and is covered by a thin layer of the external 

 membrane of the vesicle. (PL XVI. fig. 13, E.) The head proper, and the pedicle, 



