314 ANNELIDA 



setae in pairsy^ close together; 3 pairs of spermathecae in segments 

 1), 10, 11; 4 pairs vesiculae seminales: terrestrial; cosmopolitan. 



H. palustris* (H. F. Moore). Length 7 cm.; segments 100; color 

 red; clitellum on segments 23 to 28; 2 pairs vesiculae seminales; no 

 spermathecae: Pennsylvania to North Carolina; in wet soil. 



4. EiSENlELLA Michaelsen (Allurus Eisen; Allolobophora Eisen). 

 Peristomium incompletely divided by prostomium (Fig. 494), clitellum 

 beginning with the segment 23 or in front of it; male pores on segment 

 11 to 15; gizzard confined to segment 17; 4 pairs vesiculae seminales, 

 which do not fuse in the middle line: 2 species. 



E. tetraedra (Savigny). Color yellow, brown, or blackish; hinder 

 and middle portions of body rectangular; length 5 cm.; thickness 4 mm.; 

 segments 90; male pores on segment 13, female pores on segment 14; 

 clitellum on segments 22 or 23 to 27: cosmopolitan; in wet soil. 



Order 3. ECHIURIDA.! 



Thick-bodied, cylindrical annelids in which the segmentation is 

 wanting or indistinct in the adult. The animals are, however, born as 

 typical trochophore larvae and at an early period of the metamorphosis 

 have fifteen rudimentary somites. Parapodia and cephalic appendages 

 are wanting. A pair of large setae is present on the ventral side near 

 the forward end; in Echiurus two groups of setae are also present at the 

 hinder end. 



The formation of the head is peculiar. The prostomium is very 

 much elongated and forms a long spatulate or trough-like structure in 

 front of the mouth, which may be very elastic and forked at the end. 

 The grooved ventral surface of the prostomium is ciliated and in it the 

 minute animals which constitute the food of the worm are swept into 

 the mouth. The prostomium is called the proboscis. 



The alimentary canal is much longer than the body and terminates 

 with the anus at the hinder end; joining the rectum is a pair of long 

 cylindrical anal pouches which communicate with the body cavity and 

 are modified nephridia. From one to three pair of typical nephridia are 

 also present in the forward part of the body. The vascular system con- 

 sists of a dorsal and a ventral longitudinal blood vessel, w^hich join each 

 other anteriorly, and no lateral vessels. The nervous system includes 

 a ventral chord which is segmented in tlie early developmental stages 

 but unsegmented in the adult. A distinct brain is wanting, but an 



* See "On tlie Structure of Biiuastus palustris, a New Oligochsote," by II. F. 

 Mooro, Jour. Morph., Vol. 10, p. 473, 1895. 



t See "Tliallaseina mellita," by II. W. Conn, Stud. Biol. Lab., J. H. U., Vol. 3, 

 1884. "North American Echiurids," by C. B. Wilson, Biol. Bull., Vol. 1, p. 1G3, 1900. 



