20 



have also observed this fact, but the movement always seemed 

 to me of an irregular and involuntary kind, not nearly so 

 vigorous as that of the Diatomacese, which Professor Max. 

 Schultze has shown to be caused by protoplasm coming out of 

 and re-entering minute perforations in the shell of the Diatom. 



The most extraordinary phenomenon exhibited by some of 

 the Desmidieae is that swarming of zoospores mentioned above. 

 I have observed it in the genera Docidium and Cosmarium. 

 The zoospores in the Desmid appear to be endowed with 

 tumultuous life, and the motion can be compared only to the 

 swarming of bees. But although this motion has been claimed 

 as a proof of animality, it has never been observed in any 

 undisputed animal organism, whilst it has been frequently 

 seen in several species of Confervoid Algse. My own observa- 

 tion extends to a specimen of the Draparnaldia Nana obtained 

 from the North Esk Eiver. I made a note of the process at 

 the time which I will here transcribe, — " Within each cell of 

 the plant there were several small dark vesicles interspersed 

 throughout the endochrome. These vesicles moved about. 

 The branches of the plant fell from their pristine erect position 

 as if overcome by the weight of the endochrome, or, as if the 

 cell walls might be decaying. Then the endochrome in each cell 

 divided into two portions, within each of which were some of 

 the dark moving vesicles above mentioned. These two 

 divisions of endochrome rapidly assumed an oval form, and 

 obtained a surrounding of cellulose. Presently each evinced 

 agitation as if suddenly endowed with life, and they com- 

 menced to revolve and beat from one side to the other of the 

 containing cell as if anxious to escape. In a minute or two 

 more their cell burst, and they shot out twirling round and 

 round, rushing hither and thither as if in ecstasies at their 

 newly acquired life power. After from five to ten minutes of 

 this display of active life they became more sober and gradually 

 assumed a quiescent state, some resting singly, but the greater 

 number aggregating." It is a marvellous sight. You are 

 watching a beautiful but inert plant ; suddenly its branches 

 droop, and as suddenly the contents of each cell became 

 endowed with impetuous, tumultuous, exuberant life. 



Each frond in the Desmidieae is a single cell, and each cell 

 has a suture, in some species hardly recognisable, in others the 

 constriction is so deep as to extend almost entirely across the 

 cell, the segments being joined only by a narrow isthmus 

 giving it the appearance of two cells instead of one. That 

 the frond is a single cell there can be no doubt, however much 

 appearances in some species (vide Micrasterias, Euastrum, 

 Cosmarium) may lead one to think otherwise. The proof that 

 there is no septum between the segments is readily seen, for 



