304 MR GOODSIR ON THE ULTIMATE SECRETING STRUCTURE, &c. 



certain secreting membranes. Thus the membranes which secrete the purple of 

 Aplysia and Janthina are not covered with a continuous layer of purple secreting 

 cells, but over the whole surface, and at regular distances, there are spots, consist- 

 ing of transparent, colourless nucleated cells, around which the neighbouring cells 

 become coloured. Are these transparent cells the germinal spots of these secret- 

 ing membranes ? And may not the walls of the elongated tubes, and the surfaces of 

 the laminae within certain glands, have a similar arrangement of germinal spots ? 



We require renewed observations on the original development of glands in 

 the embryo. From the information we possess, however, it appears that the pro- 

 cess is identical in its nature with the growth of a gland during its state of func- 

 tional activity. 



The so-called blastema, which announces the appro aching formation of a gland 

 in the embryo, in some instances precedes, and is in other instances contempora- 

 neous with, the conical blind protrusion of the membrane upon the surface of which 

 the future gland is to pour its secretion. 



. In certain instances it has been observed that the smaller branches of the duct 

 are not formed by continued protrusion of the original blind sac, but are hollowed 

 out independently in the substance of the blastema, and subsequently communi- 

 cate with the ducts. 



It appears to be highly probable, therefore, that a gland is originally a mass 

 of nucleated cells, the progeny of one or more parent cells, mediate or immediate 

 products of the yelk ; that the membrane in connexion with the embryo gland may 

 or may not, according to the case, send a portion of the membrane, in the form of 

 a hollow cone, into the mass ; but whether this happens or not, the extremities of 

 the ducts are formed as closed vesicles, and then nucleated cells are formed within 

 them, and are the parents of the epithelium cells of the perfect organ. 



Dr ALLEN THOMSON has ascertained that the follicles of the stomach and large 

 intestine are originally closed vesicles. This would appear to shew that a nucle- 

 ated cell is the original form of a follicle, and the source of the germinal spot which 

 plays so important a part in its future actions. 



The ducts of glands are therefore inter-cellular passages. This is an import- 

 ant consideration, inasmuch as it ranges them in the same category with the inter- 

 cellular passages and secreting receptacles of vegetables, 



I conclude, therefore, from the observations which I have made 1st, That all 

 the true secretions are formed or selected by a vital action of the nucleated cell, 

 and that they are first contained in the cavity of that cell ; 2d, That growth and 

 secretion are identical the same vital process, under different circumstances. 



