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THE GENUS CHLOROCHYTEIUM. 



11 



separated from one another by colourless strands ot cytoplasm, aiul a few 

 small pyrenoids are scattered throuo-Ii the coll. The nucleus is bounded by 

 a nuclear membrane, and contains a single very large karyosome and a 

 nuclear network in whicli are imbedded a few distinct granules ; these, 

 however, do not appear to be composed of chromatin. A quantity of starch 

 is present in the form of small granules scattered throughout the cell. 



Though the structure of the vegetative cell thus bears a striking resem- 

 blance to that of C. Lemna\ yet the mode of zoogonidia^formation differs 

 considerably, and it is upon this character that the separation of the two 

 species mainly depends. The chlorophyll-containing portion of the cytoplasm 

 contracts from the cell-wall and forms a more or less irregularly globular, 

 homogeneous^ green mass in the centre of the cell, and the space between 

 this central mass and the cell-wall is seen to be filled with a laro-e number 

 of orange- or reddish-coloured granules. Even before it is properly rounded 

 off the central green mass divides by constriction into two piirts, and by a 

 further successive bipartition of each of these eventually a lar^e number of 

 rounded bodies arise, each of which finally acquires cilia and becomes a zoo- 

 goindium. During this process of division a rejuvenation of ihe protoplasm 

 takes place, so that the completed zoospores entirely fill the cell-cavity. At 

 the same time the coloured granular substancCj which at first completely fills 

 the spaces between the naked daughter-cells, gradually decreases in quantity 

 until at the time of the liberation of tlie zoospores it has almost entirely dis- 

 appeared, though a few scattered granules may in some cases be observed. 



This niode of zooo;onidia- formation is identical with that described by 

 Klebs for Scotlnospluera^ and differs from all other methods observed in allied 

 species^ except perhaps that described for C FacciolacG (Borzi), in the 

 secretion of the red pigment. This very characteristic process has never 

 been recorded until the present since it was first described by Klebs in 1881, 



for though Spencer Moore thought he had found the alga growing in Lemna 

 trisulca in 1884, he based his identification entirely on the vegetative 

 characters of the cell since he found no reproductive stages. 



The biciliate zoogonidia are extruded througli a hole formed by the 

 distintegration of a small part of the zoogonidangium-walL They are set 

 free separately without any mucous vesicle, and very quickly come 

 to rest without fusing. AVhen first extruded from the mother-cell the 

 zoogonidia are spindle-shaped, with a single chloroplast which is usually pos- 

 terior in position, but which may form a parietal band round the zoo^^onidium, 

 leaving a colourless, posterior^ pointed apex ; a small reddish pigment-spot 

 is frequently to be seen in the anterior colourless part of the zoogonidium. 

 After swimming about for a few moments the zoogonidia become attached by 

 their cilia to one of the blue-green filaments, and by a contraction of the 

 cytoplasm they become j)ear-shaped, with the chloroplast fitting close against 



