1894.J MICROSCOPICAL JOURNAL. 205 



To better illustrate the motion of the motile spherules 

 of the Surirella, I could not easily recall any similar or 

 analagous movements, except that seen when one ob- 

 serves colonies of tadpoles, in clear water braiiches, 

 where the tadpoles may be seen in shallow places in 

 crowded groups. At such a time, it will be noted, that 

 there is a continual darting about, or mutual crossing to 

 opposite groups, across an intervening space ; but, in the 

 case of the motile spherules, the source of the propelling 

 power evades the lens. I suspect that if the spherules 

 could be examined after chance extrusion from the frus- 

 tules, a flagellum, as in the case of Monas termo, might 

 possibly be demonstrated with a suitable power. The 

 reader will thus perceive that a variety of vital proper- 

 ties, and varied morphological phenomena are exhibited 

 by a Surirella, during the course of its life cycle. This 

 preponderance of intelligent and consecutive phases of 

 protoplasmic and molecular activity encourages me to 

 believe that the construing of all these varied vital phe- 

 nomena, of such a simple nature as to lower them to 

 the simplest forms of plant life, is done in contravention 

 to their highly complex organization, as compared to 

 many of the Infusorians classed under the Protozoa. 



In the material secured for the use of the studies em- 

 braced in this paper, I had occasion to observe many 

 kinds of Infusorians, Desmids and Rhizopods, and as the 

 living Diatoms were more particularly my object of 

 study I was enabled to study species of the following 

 genera, viz; Surirella, Navicula, Nitzschia, Eunotia, Bac- 

 illaria, Cyclotella, Synedra ; and in six of these genera, 

 I ascertained the absolute indication of the contractile 

 and retractile power of the investing ectoderm or man- 

 tle of exoplasm, without the aid of staining agents or 

 pigments, but simply by watching their travelling mo- 

 tions through the water on the slide. This method 

 alone is sufficient for all purposes of demonstration of 



