ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. 73 



imperfect capillary network. In the more advanced animal, 

 when the capillary network is consolidated, the product of 

 solution of the textures passes or drops into the intercellular 

 or textural lacunae, which appear to be the radicles of the 

 lymphatic system ; a system which in the adult communicates 

 with the blood-vessels only at a few places in the neighbour- 

 hood of the trunks of the original blastodermal veins. 



The blastoderma may be considered therefore not only as 

 the first form which the being assumes after the commence- 

 ment of development, and as a basis out of and in which its 

 higher structures are to be raised, but also, as has been already 

 stated, the organ of primary digestion that is, of the appro- 

 priation arid elaboration by the individual of nutritive matter 

 already prepared, to a certain extent, by another individual or 

 organ. 



All the principal organs and parts of the future being are 

 formed in, and out of, portions of the blastoderma. The 

 laminae dorsales, the cerebro-spinal axis, the visceral laminae, 

 the intestinal tube, heart, and liver, derive their origin from 

 this source. Their original relation to this part is soon lost 

 sight of from changes in their positions, but principally from 

 the increased development of their original blastema, and its 

 change into the various textures, and from the various arrange- 

 ment of these textures in the organs. 



There are three organs, however, which still retain their 

 primitive structure after all the other parts of the animal have 

 undergone their complete development, so as finally to exhibit 

 no trace of their original simple texture and arrangement. 

 These organs are the supra-renal capsules, the thymus, and 

 thyroid. 



The structure of each of these three organs is essentially 

 the same : they consist of masses of nucleated cells. These 

 cells are grouped around numerous germinal spots arranged 

 throughout the mass, and which may be supposed to act as 



