in] GREEN CELLS OF CONVOLUTA 85 



some of irregular form. As the animal moves along, 

 its muscles contract and the shapes of the green cells 

 change somewhat (cf. Fig. 14). Seen under a higher 

 power, the green cells present the appearances indi- 

 cated in Fig. 17. Each cell or protoplast is made 

 up of a large green, and a small colourless part. 

 The former consists of the chloroplast, the latter of 



F:G. 



Fig. 17. Cross- section of the superficial tissues of Convoluta roscoffen- 

 sis. G .C. = green cells in rows. N = nucleus of green cell. Py r = 

 pyrenoid. Mes.C.=r nucleus of attendant cell. F.G. = fat granules. 

 CM = cilia at the surface of the animal. Ep = epidermis. 



colourless protoplasm. Embedded in the mass of 

 colourless protoplasm, but not visible without special 

 methods of preparation, is a denser, oval body, the 

 nucleus which is an integral part of plant and animal 

 cells. Lying in the chloroplast is a dense body sur- 

 rounded, halo-like, by a clearer margin. This body, 

 which is called a pyrenoid, consists of proteins and is 



