DEFINITION OF BOTHKIOCEPHALUS C0RDATU3. 



737 



usually project from the surface, and are draivn out longitudinally on 

 either side, into a deep and sharply defined suctorial groove. Behind 

 this head extends, not a long, narrow, neck-like anterior portion, hut 

 the h'oad hody with its segments, which arc from the first readily 

 recognisable iy the naked eye, and which increase in size so quickly that 

 the worm acquires anteriorly a lancet-like form. At a distance of 3 cm. 

 iehind the head, the joints arc already sexually mature, and 3 cm. 

 farther back they have attained almost their maximum treadth (7 to 8 

 mm). The number of immature joints is at the most about 50, and the 

 great majority of these exhibit distinct genital apertures. Their imma- 

 turity consists only in the absence of hard-shelled ova. There is no dis- 

 tinction betiveen median and lateral regions in the immature joints. 

 These only become distinguishable with increasing maturity, when the 

 median have a clear appearance, while the lateral portions are a dark 

 grey colour, which gradually becomes more and more marked. The 

 length of the mature joints is on an average between 3 and 4 mm., but 

 the contractility of the worm is so great that they sometimes measure only 

 1'3 mm., with a corresponding increase in breadth and thickness. Only 

 the terminal joints are exceptional, in having generally a square form, 



Tig. 395. 



Fig. 394. 



A B 



fe4 



rrnr 



r-Lam 



Fig. 396. 



Fig. 394.— Head and anterior portion of BothriooephaZus eordatus, seen (A) from the 

 side, and (B) from the surface. ( x 5.) 



Fig. 395.— a number of mature joints of B. eordatus (nat. size). 

 Fig. 396. — Uterus of B. eordatus (nat. size). 



measuring each way 5 to 6 mm. In the largest ivorms, 115 cm. long 



(with a head 2 mm. long, and broad), there are about 600 joints, but the 

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