ON PELOMTXA VIRIDTS. 359 



with a low power such regions naturally appear dark, but 

 with polarised light they appear as bright spots, owing to the 

 doubly refracting character of the sand particles. A number 

 of these particles is always present, but at times their number 

 is so enormous that there is almost as much sand as proto- 

 plasm. I have watched an individual so filled collect the 

 greater number of these particles at one spot^ and then simply 

 pour them out from the protoplasm. An individual may thus 

 get rid of hundreds of these particles in a minute or two, but 

 the process of collecting them together preparatory to their 

 extrusion is slow. I believe that there is a periodical whole- 

 sale extrusion of these particles. These particles have all the 

 appearance of sand ; they are of very varying size and of very 

 irregular shape, and are insoluble in all ordinary reagents ; 

 they are crystalline in nature, and, as stated above, are doubly 

 refracting. 



The presetice of these particles has not, I fancy, any special 

 significance, they occur in great numbers in the mud and 

 are taken in with the food ; the animal, indeed, seems to exercise 

 no discretion as to what it takes in. They become collected 

 together as a mechanical result of slight movements, and wheu 

 the animal makes some more extensive movements are thrown 

 out in great numbers. 



Structure of the Protoplasm. 

 Viewed with an ordinary high power of the microscope the 

 main mass of the organism appears of a green colour, while at 

 the periphery, from time to time, perfectly colourless regions 

 may be seen. One's first impression is that there is a green 

 endoplasm and a colourless exoplasm (figs. 2 and 3). With 

 the same magnifying power, in addition to the various proto- 

 plasmic contents described elsewhere, what appear to be 

 granules may be recognised abundantly distributed through 

 the greater mass of the protoplasm. The colourless peripheral 

 regions above mentioned are usually devoid of these granules. 

 The granules all prove upon further examination to be bacteria, 

 and but for their presence the protoplasm itself would appear 



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