NATURAL HISTORY OF BHOMPSTON POND. 207 



contractile vacuole (j), and staining reveals a micronucleus as 

 well as the somewhat horse-shoe shaped meganucleus (k). 

 The writer has watched the process of reproduction by fission. 

 At first the disk is cleft, which is followed by a complete 

 division of the body into two parts (fig. 14, 1), one of which 

 acquires a posterior set of cilia, while the anterior spiral of 

 cilia disappears. This portion at last breaks away from the 

 stalk and, by means of the posterior set of cilia, swims away 

 to settle and found a new colony elsewhere (m). The other 

 part remains on the old stalk and continues living as before 

 the division. 



A colonial form, Epistylis (fig. 16), occurs in this pond in 

 dense clusters attatched to certain aquatic animals, for 

 instance, on the shell of Planorbis, and on Cyclops. It chiefly 

 differs from Vorticella in that the stalk (a) is branched and 

 non-contractile . 



Of all the micro-organisms perhaps Coleps (fig. 17) is the 

 most ravenous, dense clusters of them being frequently 

 found eagerly devouring dead infusoria. This isolated form, 

 whose systematic position is not settled, is barrel-shaped, 

 with the carapace plainly marked, with both transverse (a) 

 and longitudinal grooves (b) containing cilia. The anterior 

 end terminates in dentate projections (c), while posteriorly 

 the carapace is furnished with three short terminal spines (d). 

 In swimming they revolve on the long axes of their 

 bodies, and quickly collect around and devour a crushed 

 infusorian. 



Euglena viridis (fig. 18) may be considered as standing, 

 between the animal and plant kingdom, being claimed alike 

 by zoologists and botanists. On the one hand the cell seems 

 to be enclosed in a flexible cuticle (not a cellulose covering), 

 and it ingests solid food, on the other hand the cell contains 

 a mass of bright green chlorophyll granules, which it uses for 

 the photosynthetic formation of carbodydrates, grains of 

 paramylum being found in the protoplast. The latest 

 researches show that this organism has the power of con- 

 structing its own chlorophyll. The spindle-shaped body 



