288 



AQUATIC MICROSCOPY FOR BEGINNERS. 



black, with yellow dots, the legs being shorter than 

 the body, and black, with red ends. In another the 

 body is red, with two pairs of dark red eyes, and 

 long legs. The young are said to have but three legs. 



4. Eylais (Figs. 191, 194). 



The two anterior coxae are in contact by their entire 

 length, and form one group on each side. The two 

 posterior are in contact only as described in the Key 

 and shown in the figure. They are all moderately 

 narrow. The mouth is round, ciliated, and with a 

 kind of hood which the beginner may have some 

 trouble to recognize. The ventral plates are curved, 

 almost crescentic, and narrow, one being on each side 

 of the ventral opening, while just behind them are two 

 small tracheal apertures. The intestinal orifice is 

 visible at the rear in the middle line, with a tracheal 

 opening on each side. The eyes are four, in two 

 pairs, rather close together. A large red, nearly 

 spherical Eylais' is common in our ponds. The young 

 are described as being red, transparent, with four eyes 

 wide apart, and six legs. 



Fig. 194.— Coxae Fig. 195.— Coxae of Fig. 196.— Coxae 

 riydrdchha. of Eyliis. Arreniirus (female). of Arremirus 



(male). 



5. ARRENtJRUs (Figs. 195, ig6). 



The coxEB form two groups on each side, the two 

 anterior being in contact by their entire length, as are 



