540 THE NATURAL HISTORY OF 



There are, however, forms in which the enveloping 

 membrane cannot be distinguished at all, and in general 

 does not exist : these forms are designated " naked 

 zoospores" (nackte Schvi^armzelle.) They are true pri- 

 mordial cells ; that is to say, their external boundary is 

 formed of nothing but the contractile cell-contents, or 

 protoplasm ; a true, solid, and rigid vegetable cell- 

 membrane is vv'holly wanting. They thus correspond in 

 their structure with the zoospores of most of the other 

 Algse {Vaucheria, (Edo^onium, &c.) These naked zoo- 

 spores originate in various ways, and belong to various 

 stages of development. The following varieties of this 

 kind of primordial cell may be distinguished. 



1. Those which differ from the encysted only in the 

 absence of the enveloping cell. This form corresponds 

 with the younger condition of the encysted zoospore, 

 arising from the division of the cell, around which the 

 enveloping cell is not yet formed. 



2. Another form arises immediately from the still cell, 

 distinguished by its verrucose figure, and its, for the 

 most part, cinnabar red colour. It is of small size, 

 and, narrow in shape (Fig. 33.) On " deliquescence" 

 taking place, the primordial cell becomes expanded, and 

 at the same time flatter and of a lighter colour, the 

 coagulated red droplets exhibiting a lively molecular 

 motion in the interior. In this case, also, large colour- 

 less vesicles are then developed in the interior. 



In certain conditions, this form of primordial cell 

 resembles, in its form and aspect, the genus Astatia of 

 Ehrenberg. 



8. Are very minute naked zoospores, not more than 

 0-002'" to 0-005'" in size, mostly globular. They con- 

 tain chlorophyll granules and red droplets, more rarely 

 chlorophyll-vesicles, and colourless granules of unknown 

 nature, as described above (Fig. 41.) 



4. Perhaps the most remarkable of all the numerous 

 aspects presented by Protococcus pluvialis, is the form of 

 naked zoospore named by Flotow Ilamatococcus porphy- 



