EXPLANATION OF THE PLATES. 



/. The thick-walled peculiar sac. 



g. Pyriform sac, a receptacle for the ova. 



i. Male organs. 



The figure also presents the arrangement of the dermal 

 spines, and the general form of the animal. 



PLATE XL page 482. 



Fig. 2. The anterior extremity and suctorial mouth of Neuronaia 

 monroii more highly magnified. 



Fig. 7. The cyst of Neuronaia monroii in a bundle of nervous fila- 

 ments. The fissured appearance of the cyst, with its epithelia, 

 is represented in this drawing. 



I am inclined to believe that the function of the cyst in 

 this and the other Cystic Entozoa is to supply nourishment 

 to the enclosed animal, drawing it from the surrounding 

 parts, and throwing it into the cavity, the structure and 

 action being identical with that in the encysted tumours as 

 already described. 



The bulbous extremities of the cysts of Trichina spiralis 

 contain masses of germinating cells, to which I am inclined 

 to attribute the same function. 



Figs. 8, 9, 11. The clavate extremities of the cysts of Trichina spiralis, 

 with their germinating absorbent cells. 



The epithelium and absorbent cells of the cysts of the 

 entozoa may be considered as permanent yelk-cells in the 

 economy of these persistent embryos. 



Figs. 1 and 3. Magnified drawingsj of Sarcina ventriculi described, but 

 badly figured by me in the Edinburgh Medical and Surgical 

 Journal, No. 151. I am still of opinion, notwithstanding 

 the arguments of Mr. Busk, in the Microscopical Journal, that 

 this body is a vegetable parasite, its sudden occurrence and 

 sudden disappearance being not more extraordinary than the 

 rapid development of many cellular structures ; the glandular 

 epithelium, for instance, during secretion. That it is a 

 Gonium, as has been suspected by Professor Link, appears to 

 me improbable, as would be admitted, I believe, by that 

 great botanist, if he had had an opportunity of observing its 

 peculiar vegetable aspect, so different from that of an in- 

 fusorial animal. 



