48 On the Nutritive and Excretory Processes of Porifera. 



XII. — On the Nutritive and Excretory Processes of Porifera. 

 By Aethur T. Masterman, B.A., Assistant-Professor of 

 Natural History, University of St. Andrews. 



Since the publication in the June number of this Magazine 

 of my short paper upon the above I have, through the 

 courtesy of Mr. Gr. Bidder, of the Naples Zoological Station, 

 been put in possession of a paper of his upon the same subject 

 (Proc. Roy. Soc. vol. li.). Before arriving at my own 

 results I had inadvertently overlooked this important work ; 

 and my conclusions in several points bear out those stated 

 by him. 



Firstly, he finds that " In Heterocozla the collars of the 

 collar-cells are at first mere fringes, which help to retain the 

 food and filter the water as it passes from the base of the cell 

 to the moving tip of the flagellum. When the cell is satiated 

 the flagellum ceases to move and degenerates ; the collar 

 unites with the neighbouring collars to prevent the water 

 that is already filtered and already foul from returning past 

 the inactive area to pollute the afferent water-supply. When 

 the food has been digested the cells elongate and become 

 closely pressed together; the separation of their basal parts 

 takes place in the manner already described (' In Leucandra 

 aspera and Sycon raphanus the collar-cell, after it has accumu- 

 lated a certain quantity of spherules in its base, splits off 

 this base by a transverse fission as a non-nucleated mass of 

 protoplasm, which we may term a "plinth " ' — p. 477), and 

 the distal parts start on a new cycle with hungry protoplasm, 

 active flagella, and separated collars." 



This conclusion only differs from that at which I arrived 

 in the fact that I have reason to believe that in the case I 

 examined the whole collar-cell degenerates to the amoeboid 

 condition. The process here described by Bidder is obviously 

 a stage in the differentiation of the endoderm cells into loco- 

 motor}' permanently collared cells, and permanently amoeboid 

 (so-called " mesodermic ") digestive cells which I suggested 

 as being probable in the higher sponges (p. 495), just as the 

 separation of any organ performing any two main functions 

 into two distinct organs, each performing one of these func- 

 tions, will be preceded by steps in which the primary organ 

 will be divided into two parts more or less distinct, each 

 performing mainly one function, the separation of the two 

 functions taking place by degrees in time and space (cf. uro- 

 genital organs and differentiation of sexes). 



The above author also describes and figures " Metschnikoff 



