262 THE MICROSCOPE. 



The existence of delicate threads passing from the 

 central mass to the enveloping cells, and the appearance 

 occasionally of little particles having molecular motion, 

 serve to show that the contents .of the enveloping cell are 

 less of a gelatinous consistence, than of a fluid nature. 

 And the continuity of the primordial cell-wall with the 

 filaments proves it is surrounded only with a layer of 

 protoplasm, and is not inclosed in a dense membrane 

 of cellulose. The most distinctive characteristic of the 

 primordial cell, and what appears to constitute its most 

 essential importance in the life of the cell in general, but 

 particularly in that of the zoospore, consists in its being 

 the contractile element of the vegetable organism that 

 is to say, that from an intrinsic activity it possesses the 

 faculty of altering its figure, without any corresponding 

 change in volume. 



The Protococcus pluvialis has true motile organs, 

 namely, two long vibratile flagella arising from the pri- 

 mordial cell (fig. 144, B, a), which, passing through two 

 openings in the enveloping cell, move about in the water. 

 These organs, during the life of the cell, move so 

 rapidly, that it is then difficult to perceive them ; they 

 are recognized by the currents produced in the water ; 

 as death approaches motion slackens and they become 

 evident enough. They are also rendered very distinct by 

 iodine. They are always protruded about the extreme 

 point of the conical elongation, at the anterior end of the 

 primordial cell, and in such a manner as to appear to be 

 mere continuations of its substance. Since these pro- 

 cesses consist of protoplasm, it is evident that the flag- 

 ella must be regarded as composed of the same sub- 

 stance. They resemble, in some respects, the so-called 

 proboscis of certain Infusoria, such as Euglena and Ifo- 

 nads, and do not differ very materially from the non- 

 vibratile, retractile filaments of Acineta and Actinophrys. 



It Is only that portion of the vibratile filaments beyond 

 the enveloping cell that exhibits any motion, the portion 

 within the outer cell being always motionless, and in that 

 part of their course the filaments appear to be surrounded 

 with a sheath. This seems to be the case, not only from. 

 the greater thickness at that part, but also from the cir- 



