NATURAL HISTORY OF BHOMPSTON POND. 209 



roughened areolated carapace (a), which is very transparent 

 and flattened, bearing four spines anteriorly and two poster- 

 iorly. It is about l-100th in. in length ; it has no eye spots, but 

 possesses a very mobile foot terminating in two toes (b). It 

 is found chiefly in the sediment in most parts of the pond, 

 together with two others of this family Brachionus (fig. 23), 

 with a single eye spot (a) and smooth carapace (b), and 

 Anuraea (fig. 24), with a single eye spot (a), but no foot. The 

 curious little rotifer known as Mastigocerca (fig. 25) is note- 

 worthy on account of its asymmetry. The lorica bears an 

 asymmetrical dorsal crest (a), and the foot is represented by 

 one of the toes, which is as long as the rest of the body (b), 

 while the other toe is extremely small (c). Even the mastica- 

 tory organs display a want of symmetry, the left part being 

 more developed than the right. The mastax (d) is very 

 elongated, and there is a single eye spot (e). Euchlanis 

 (fig. 26), a form with a large lorica, which is open on the 

 ventral surface, occurs sparingly in some parts of the pond. 

 More frequent, however, is an allied species of Lepadella 

 (fig. 27), with a somewhat flattened carapace and a foot 

 ending in two toes. Lepadella is a very small rotifer, its 

 total length being only about 1 -500th in. Another member of 

 this family, Salpina (fig. 28), differs from the last, in that it 

 possesses a three-sided carapace, closed below and terminating 

 posteriorly in spines (a). The foot is forked and a single 

 cervical eye spot is present. Rotifer vulgaris (fig. 29) is 

 common in most parts of the pond. Its general form, its 

 leech-like and rotating movements, are too well known to need 

 description. 



Isolated from the Rotifera is a small group of allied animals 

 (Gastrotricha) well represented by Chaetonotus (fig. 30). The 

 body is elongated, the convex upper surface bears curved 

 hairs (a) and the flat ventral surface is covered with 

 cilia. The mouth is situated at the rounded anterior end, 

 while it has a characteristic bifurcated extremity (b) at the 

 opposite end. The direction of the undulating swimming 

 movements are regulated partly by flexion at the neck. 



