ON MEGASOOLEX CCERULEUS. 65 



branches of the dorsal vessel ; noue of the other branches of 

 the dorsal vessel, either those anterior or those posterior to 

 these eight, are contractile. 



The three anterior pairs lying in segments vi, vii, and viii 

 are lateral hearts ; while the five posterior pairs lying in seg- 

 ments IX to XIII are latero-intestinal hearts, i. e. they are 

 connected equally with the dorsal and the supra-intestinal 

 vessels of their respective sides. An examination of fig. 5 will 

 show that the dorso-iutestinal vessels of segments xiv to xvi 

 have similar connections, but they do not appear to be rhyth- 

 mically contractile, nor have they the peculiar sphincter 

 muscle at their distal extremities that the hearts have.^ 



The hearts of segment vi arise immediately in front of 

 septum VI . VII (each pair of hearts arises immediately in front 

 of the septum which divides the segment in which they lie 

 from the segment next following). They extend only for a 

 short distance on the wall of the gizzard, and terminate in a 

 muscular bulb (figs. 4 and 6, /), a sphincter which is shut 

 during the diastole, and opens at the systole of the heart. 

 This heart is not connected with the ventral vessel. Two 

 branches arise at its extremity, just beyond the muscular bulb. 

 No branches arise directly from any of the hearts, i. e. between 

 the point of connection with the dorsal vessel or dorsal and 

 supra-intestinal vessels, as the case may be, and these muscular 

 bulbs. The two branches above mentioned break up into 

 capillaries on the walls of the gizzard, the network being con- 

 nected, on the other hand, with branches of the anterior 



memoir, and observed by myself in many other Perichsetidae). In all recorded 

 cases in which there are some hearts which do not communicate alone with 

 the dorsal vessel, such hearts are the posterior ones of the series. 



I adopt Perrier's term lateral hearts for those which communicate with 

 the dorsal vessel only, and his term intestinal hearts for those which com- 

 municate with the supra-intestinal vessel only, and shall use the term latero- 

 intestinal hearts for those which have the dual connection to indicate tha 

 they correspond to both lateral and intestinal hearts. 



1 These peculiar relationships show how useless it is for classificatory 

 purposes to record simply the number of pairs of " hearts," as is often done, 

 without detailed account of what vessels are so named. 



VOL. XXXII, PART I. — NEW SEli. E 



