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



During the sixth stage the central cell has disappeared, and has apparently 

 become the external covering of another family of young cells. (PI. XVI., fig. 6, 

 D G.) This little mass is nodulated, its component cellules not having yet sepa- 

 rated from their common centre. There are now within the original germinal 

 vesicle two concentric circles of cells, the innermost of which are scarcely formed. 

 During the next stage the central nucleus for the third circlet of cells makes its 

 appearance, with its accompanying clear central space (PI. XVI., fig. 6', F G), soon 

 becomes nodulated, and shortly throws off a third circlet of young cells. 



The formation proceeds in this way for a longer or shorter period ; the young 

 cells are always formed from a central nucleus (PI. XVI., fig. 7, A) ; and as they 

 increase in size, arrange themselves in concentric circles, pushing the previous 

 generations always farther from the centre of production. While this mode of 

 growth is proceeding, the external membrane of the gemmule increases in size 

 and thickness, apparently by a deposition of new matter, as the young cells are 

 produced. 



Up to this period the development has proceeded in one plane, the gem- 

 mule being a flat disk with a germinal spot in its centre. (PI. XVI., fig. 7, A.) 

 It is situated, as has been already stated, between the two layers of the cyst of 

 the parent Hydatid, and has now acquired such a size as to project slightly from 

 the surface (PI. XVI., fig. 9) of the cyst, and to push, as it proceeded in the lateral 

 direction, a fold of the external membrane before it ; which membrane also be- 

 comes thicker in the neighbourhood of the gemmule, in consequence of the addi- 

 tion of new folds and fresh deposition. (PI. XVI. fig. 11, B.) 



It has already been stated that the development of the gemmule had pro- 

 ceeded in one plane only from one central germinal spot. In this way a base is 

 formed for the future pedicle and head (PI. XVI., fig. 11, B), for at this stage the 

 gemmule projects very slightly from the surface of the Hydatid. The develop- 

 ment now ceases in the lateral direction, and commences in a direction perpendi- 

 cular to the original plane. (PI. XVI., fig. 11, A.) For the sake of clearness, I 

 have termed the former of these the (Jiscoidal, and the latter the vertical period of 

 development ; although each of these may be again divided into intermediate 

 stages. Along with this change of direction additional germinal centres appear. 

 (PL XVI. fig. 8, D.) I have not observed more than three of these centres, and 

 have been unable to ascertain their actual number ; probably they vary as to num- 

 ber, seeing that all the cells which are henceforth formed are productive, and, of 

 course, all tend to form centres. From these additional centres fresh families of 

 cells are constantly being produced, which again, in their turn, afford new centres; 

 the increase of the mass being kept within certain limits apparently by the solu- 

 tion of the peripheral cells of each centre. It will be observed that the simi- 

 larity between this development and that observed by Dr MARTIN BARRY, in the 

 early stage of the mammalian ovum, is very remarkable. 



