in] GREEN CELLS OF CONVOLUTA 91 



cells are available for the nutrition of the tissues of 

 the animals which contain them. 



The evidence which suffices to demonstrate that 

 the coloured cells do actually make contributions to 

 the nutrition of the animals is not far to seek. If 

 C. paradoxa is examined microscopically immediately 

 after capture, it is seen that the tissues of animals 

 whose yellow-brown cells are rich in droplets of 

 reserve fat contain also large numbers of globules 

 of a similar nature (Fig. 18). Moreover, the appear- 

 ance of the fat-globules contained in the yellow- 

 brown cells suggests most forcibly that the fat lying 

 in the tissues of the animal owes its origin to the 

 secretion of fat by the yellow-brown cells. The 

 appearance of the yellow-brown cells recalls, in this 

 respect, that of cells of a mammary gland in its active 

 stage. Just as the fat contained in the milk which 

 is secreted by the cells of a mammary gland is 

 liberated in droplets by the rupture of the clear 

 vacuolated parts of the secreting cells, so droplets 

 may be seen in course of extrusion from the yellow- 

 brown cells into the tissues of the animals (Fig. 18). 

 The large, clear, anterior end of the yellow-brown 

 cell only to be seen in fresh-caught animals which 

 have been exposed in their natural habitat to a fairly 

 high light intensity contains often one, large fat- 

 globule. In some yellow-brown cells, one or more 

 droplets lie in the deeper part of the clear anterior 



