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



tions just detailed appear to me to enable us to trace the 

 functional import and anatomical peculiarities of these organs. 



During the first stage of the development of the animal 

 ovum, digestion and respiration — the absorption and prepara- 

 tion of nutriment — are carried on by the blastoderma, a struc- 

 ture consisting of nucleated cells and of vessels. 



The cells, of which the blastoderma consists, are the pro- 

 geny of that previously occupying the germinal spot of the 

 ovum, and are continually reproduced and increased in num- 

 bers by the production of others from the nutritive centi-es, or 

 secondary germinal spots distributed over it. 



Materials for the nutrition of the blastoderma are derived 

 from the subjacent yelk. The matter resulting from the solu- 

 tion of a certain number of the secondary blastodermal cells — 

 that is, of the progeny of the primary blastodermal cellSj or 

 nutritive centres — is employed by the nutrient matter of the 

 remaining secondary or proper blastodermal cells. In this 

 way " pabulum" is afforded for two purposes — the growth of 

 the blastoderma, and the growth of the embryo itself. 



During the early period of the existence of the blasto- 

 derma, before the circulation has been established, the product 

 of solution of the elder is at once absorbed by the younger 

 cells. During the later periods, the product of solution drops 

 into the incipient loops of the blood-vessels, and so circulates 

 for purposes of nutrition. This is an instance of primary 

 lymphatic absorption, and differs in no essential particular 

 from the same process in the animal further advanced. We 

 may consider the blastoderma in fact, during the first period 

 of its circulation, as containing very numerous lymphatic 

 ducts, instead of a few, as in the more perfect animal. 



In the blastoderma, the process by which nutrient matter 

 passes into the circulation, or the act of absorption, as it is 

 usually called, is reduced to its most simple form, being con- 

 temporaneous and also identical with the formation of the 



