INVERTEBRATA. 



409 



of the same nature as the pyrenoids of the lower Algae. 

 Other authorities do not consider the central body as a 

 pyrenoid. According to some observers, the chlorophyll 

 rods constitute a single chloroplast containing a pyrenoid 

 in the centre, so that the pyrenoid would be contained in 

 the chloroplast as is the case in Algae. The pyrenoids 

 are believed to consist of proteid substance and to be 

 accumulations of nitrogenous food material. Around the 

 pyrenoid in Euglena viridis, between the radiating chloro- 

 phyll rods are grains of paramylum of rounded or ellip- 

 soidal shape. They have a homogeneous transparent 

 appearance contrasting with the granular protoplasm. 

 The typical relations of these various structures are repre- 

 sented in fig. 203, D. Sometimes the paramylum grains 

 increase in number to such an extent that they obscure the 

 other structures as in fig. 203, B. Fig. 203, E, shows a 

 specimen in which the chloroplast consists of one long rod 

 bifurcated at its posterior extremity and evidently con- 

 tinuous with the pyrenoid at its centre. 



7. Reproduction. Euglena reproduces only by simple 

 cell-division ; no conjugation has yet been observed with 

 certainty in any species of the genus or of the family to 

 which it belongs. In the case of E. viridis division seems 

 to occur only in the motionless condition of the cell. The 

 cell becomes stationary and spherical, and surrounds itself 

 with a mucilaginous envelope. The flagellum disappears. 

 The pyrenoid is almost central, and large : it is surrounded 

 by paramylum grains. The nucleus is situated below the 

 pyrenoid, it is large and its chromatin granules are con- 

 spicuous. Division commences in the pyrenoid, which 

 elongates transversely and then constricts itself in the 

 middle and separates into two halves. Then the nucleus 

 divides. The nucleo-centrosome elongates transversely 

 and the chromosomes also elongating arrange themselves 

 parallel to the nucleo-centrosome, then break in the middle 

 and the nucleus separates into two. Division may be 

 Repeated several times in the resting condition so that a 

 pellicle is formed consisting of numerous motionless 

 Euglenae embedded in a mucilaginous film : such films 



