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LEON J. COLE. 



intestine, keeps the two streams apart (cf. Fig. 2, sept.). Dohrn's 

 description of the heart agrees very closely with that of Hoek, 

 it being an elongated sac with thin muscular walls, which, how- 



A 



Fig. I. A, apparent change 

 in the shape of the heart with 

 contraction and expansion, as 

 seen when viewed from above 

 in a living specimen of Endeis 

 spinosus. Solid line, diastole; 

 broken line, systole. The ar- 

 rows show the course of the 

 blood where its streaming 

 could be observed; the opacity 

 of the intestine and other or- 

 gans prevented its being seen 

 in other parts. B, a single 

 lateral ostium with valve. 



Fig. 2. Diagrammatic cross-section oi the 

 body of a pycnogonid through a pair of the 

 lateral processes, illustrating the way in which 

 the heart contracts: d.b.s., dorsal blood space; 

 d.cu., dorsal cuticula; h., lumen of heart; h.w., 

 side wall of heart (at diastole); h.w/, position 

 of side wall of heart at systole; int., main lon- 

 gitudinal trunk of intestine; int.c, intestinal 

 cecum going to leg; sept., transverse horizontal 

 septum (at diastole); sept.^, position ot trans- 

 verse septum at systole; v.b.s., ventral blood 

 space; v.cu., cuticula of ventral side, v,cu/, 

 posterior edge of underlapping cuticula of the 

 preceding segment; t.g., ventral ganglion. 

 (Based on the cross-section of a species of Nym- 

 phon figured by Dohrn, 1881, pi. 15, fig. 10. 

 The ovary, which lies between the intestinal ceca 

 and the transverse septum, has been omitted for 

 the sake of clearness.) 



ever, do not completely enclose it, the dorsal wall being formed 

 by the chitinous integument of the back (cf. Fig. 2). 



In Phoxichilidium femoratum Loman (1907) found that a 

 systole of the heart occurred two or three times each second, 

 which would be 120 to 180 contractions to the minute. A count 



