

CHAPTER XIII. 



CONCERNING THE MODIFICATIONS OBSERVED IN THE 

 CHEMICAL PROCESSES OF DIGESTION IN SOME DIVI- 

 SIONS OF THE ANIMAL KINGDOM. 



THE researches which have of recent years been made by such 

 distinguished observers as the lamented Professor Krukenberg, Pro- 

 fessor Metschnikoff and others, on the process of digestion throughout 

 the animal kingdom have been so numerous and so specialised that 

 it would be hopeless to give their results in detail without unduly 

 extending the limits of this work. The following brief notes may, 

 however, prove useful to the student of comparative physiology. 



SECT. 1. THE INTRA-CELLULAR DIGESTION OF THE LOWER 

 INVERTEBRATA. 



In certain elementary animal forms, each particle of their structure 

 possesses the same nutritive endowments as its fellows, and there is 

 no differentiation of cells set apart to discharge those chemical 

 functions which we term digestive, and which consist essentially in 

 the secretion of a juice or juices, whose function it is to render the 

 food constituents soluble and diffusible, so that these can make their 

 way into the interior of the organism and replace the matter which 

 the latter is ceaselessly losing. In the lower organisms to which we 

 refer, digestion is said to be intra-cellular. 



The simplest and, in many respects, the most typical example of 

 intra-cellular digestion is that presented by certain Rhizopods, which 

 consist essentially of a mass of living contractile, somewhat granular, 

 protoplasm with a nucleus. The earlier knowledge of the phenomena 

 associated with the ingestion and digestion of food by these unicellular 

 organisms rests on the observations of Dujardin, Kolliker, Carter, 

 Haeckel, De Bary and others, whilst we owe the most recent, com- 

 plete, and interesting facts relating to these processes, as they can be 

 observed in Amoeba proteus and Actinosphcerium, to the investiga- 

 tions of Miss Greenwood 1 , to some of whose results the attention of 



1 M. Greenwood, ' On the Digestive Process in some Rhizopods,' (From the Physio- 

 logical Laboratory, Cambridge), Journal of Physiology, Vol. vn. (18851886), pp. 253 

 273. Besides recording the results of her own observation, Miss Greenwood has in 

 this paper given an account of the earlier literature of the subject. 



OF THE 



