568 FRESH-WATER BIOLQGY 



4. Euchlanidae. Another line of divergence leads from the No- 

 tommatidae, probably likewise through Furcularia, to Distyla^ 

 Cathypna, Monostyla, and Euchlanis, — forming the family Euch- 

 lanidae. The first steps in this series are seen in those species of 

 Distyla in which the body is soft, wrinkled, and only a little flat- 

 tened (Fig. 890). In the extended condition these are hardly to be 

 distinguished from small species of Furcularia. But when re- 

 tracted there is a tendency to form lateral furrows along the side, 

 while a sharp edge is seen in front (Fig. 890, B). In other species of 

 Distyla (Fig. 891) these differentiations are permanent and the cutic- 

 ula forms an evident lorica, consisting of a dorsal and a ventral plate. 

 This line of evolution shows its highest development in Euchlanis 

 (Fig. 893). The Euchlanidae are common among aquatic vegetation. 



5. Coluridae. This group resembles the Euchlanidae, but has 

 probably developed from the Notommatidae separately. The 

 hardened cuticula here forms a soHd lorica, open at each end for 

 head and foot; sometimes the cuticula is not hardened on the 

 ventral surface. A portion of the lorica extends out over the 

 head as a sort of hood (Fig. 901). Metopidia (Fig. 901), Colurus 

 (Fig. 900), and Stephanops (Fig. 899) are the principal genera; they 

 are all minute, creeping about among plants and debris. 



6. Rattulidae. A fifth Hne of divergence leads from the Notom- 

 matidae to thegenera Diurella (Fig. 895) send Rattiilus (Figs. 896, 897). 

 The cuticula of the nearly cylindrical body becomes hardened over 

 nearly the entire surface, so as to form a curved, pipe-like structure, 

 with openings for the protrusion of head and foot. The less differ- 

 entiated RattuHdae (Diurella, Fig. 895) resemble greatly the lower 

 Notommatidae, ha\dng the cuticula only a httle stiffened and toes 

 differing but Httle from those of Furcularia. But this Kne runs into 

 extremely bizarre forms. The animals tend to become unsymmet- 

 rical, the organs of the right side being smaller, while the body 

 becomes in some cases twisted into a segment of a spiral. The 

 right toe becomes enormously extended to form a long rod-like 

 structure, while the left toe nearly disappears (Figs. 896, 897). The 

 right side of the tifophi (Fig. 898) becomes smaller than the left. 

 The Rattulidae are common among vegetation. (See the mono- 

 graph of this family by the present writer (Jennings, 1903).) 



