Maskell. — On the Neiv Zealand Desmidieas. 253 



to raise itself on end, an operation which it took four minutes to complete. 

 Having attained an upright position it remained there two minutes, waving 

 gently to and fro, and then, all of a sudden, fell over on the other side. 

 The " swarming " had now become quite violent, and the plant recom- 

 menced its travels, but this time in the contrary direction, returning towards 

 the Pinnularia ; after continuing thus for a minute or two it stopped, and 

 then once more travelled away again. For half an hour it continued 

 these manoeuvres, sometimes going one way, sometimes another, always 

 " elbowing" its way along, and in the main getting farther away from its 

 original spot. Sometimes, when it stopped, it would roll about from side 

 to side rather violently (but never from end to end). I thought I observed 

 that as the " swarming " increased, so also did the " jerks," and it appeared 

 to me also that the' endochrome was changing. It showed a tendency to 

 form in each segment two masses of closer consistency than the rest ; each 

 of these masses, retaining its bright green colour, became surrounded with 

 a brownish band, and it was in this band (never in the green particles) that 

 the swarming was conspicuous. Once an exceedingly minute Infusorium, 

 scarcely visible under the |- objective, came sailing towards the plant, some- 

 what leisurely ; but, when almost on the point of touching it, darted suddenly 

 back to some distance. Was it repelled? I could not say: it did not return. 



The oscillations and rollings of the Cosmarium continued for two or 

 three hours, and I observed that whenever it chanced to come to any little 

 mass of weed or dirt obstructing its course it avoided it, sometimes indeed 

 retracing its steps a little to get round a headland. Whenever it raised 

 itself on end I took especial pains to see whether anything could be observed 

 of the nature of cilia, or whether any appearance could be detected in the 

 water leading to the supposition that retractile processes existed, but with- 

 out success. 



I have no doubt that the movements described were quite as "volun- 

 tary," as those of any Diatom. In another part of the same slide a Stau- 

 roneis was travelling very actively and the difference between the two plants 

 was that the Diatom glided backwards and forwards without more than very 

 slight oscillation, whereas the Cosmarium made its way simply by lateral 

 jerkings. 



Staurastrum gracile, Ealfs. 



Fig. 17. 



This is another of the plants in which the differences from the European 

 form do not seem to me to be sufficient to render it distinct. As my figure 

 shows, it is less slender and the processes are shorter than in Ealfs' species. 

 Length in end view from the middle of one side to the end of the opposite 

 process (exclusive of the four spines) 50 /* : length of process 15 fx. 



