174 CALIFORNIA ACADEMY OF SCIENCES. 



adds little to the descriptions given by Wedl and 

 Kramer. Wedl found that it could be studied success- 

 fully only in living animals. According to him the 

 heart proper of Menopon pallidum is one-chambered 

 and is situated in the next to the last abdominal seg- 

 ment just below the dorsal wall. The inner cavity is 

 provided in front and behind with an opening. It con- 

 sists of a molecular parenchymous part on each side, 

 and a median membranous part. From the lateral, 

 thickened part there arise ragged prolongations remind- 

 ing one of the papillary muscles of the vertebrate 

 heart, and which terminate in fine thread-like fibers 

 attached to the median membranous walls of the heart. 

 To the outer side of the parenchymous part are attached 

 on each side a bundle of tense fibers, which may be 

 termed the right and left s.uspensory fibers of the heart. 

 The dorsal aorta has a swelling at its base forming a 

 bulbus arteriosus. This has on each side a bundle of 

 fibers, the right and left suspensory fibers of the bulbus 

 arteriosus. Likewise at the opposite end of the heart is 

 a swelling forming the bulbus venosus. This has 

 two prolongations at its posterior end which appear to 

 be inlet tubes allowing the entrance of the blood 

 into the bulbus venosus. At the posterior end is a 

 median row of fibers. 



Kramer describes the heart of Lipeurus jejunus as a 

 long narrow tube enlarged at its posterior end. Here 

 are attached the very much reduced wing-muscles. 

 "Wedl does not mention these but very probably refers 

 to them when he describes the "suspensory fibers". At 

 the posterior end, according to Kramer, are four open- 

 ings to admit the blood. Wedl states that the heart- 

 beats amount to 112-120 per minute in specimens just 

 taken from the living host, but sink to 56-52 in speci- 

 mens taken from a host that has been dead a day or so. 



