PULSATING SACS IN THE HEAD 405 



chamber of the heart diminishes in size at the end of the body, and then divides 

 into three delicate tubular vessels which pass into the three caudal appendages, 

 and extend to the end of each one, along the upper side. While the valves of the 

 heart, in all insects, are directed anteriorly because the blood flows from behind, 

 in the larva of the Ephemeridae the valves of the last chamber of the heart are 

 directed backwards, because from this chamber the blood flows in the opposite 

 direction, i.e. into the caudal appendages. During the contraction of the heart, 

 the elongated section of the same in the last abdominal segment receives a part 

 of the mass of blood contained in the last chamber, which is driven by indepen- 

 dent contractions into the caudal appendages. These vessels have openings 

 before the end through which the blood enters into the cavity of the appendages, 

 and can also pass back, in order tp be taken up by the body cavity. It is pos- 

 sible that these blood-vessels stand in direct relation to respiration. (Zimmer- 

 mann, Creutzburg, in Kolbe, p. 544.) 



The pericardial cells. Along the heart, on both sides, occur the so-called 

 pericardial cells, which differ from the fat-cells, and also the peritracheal cells 

 of Frenzel, and are mostly arranged in linear series, which have a close relation 

 to the circulation of the blood. In the larva of Chironomus, they lie in groups ; 

 in that of Culex, they are arranged segmentally. In caterpillars, these pericar- 

 dial cells are not situated in the region of the heart, but are arranged linearly 

 on the side, and form a network of granulated cells situated between the fat- 

 bodies. Other rows of these cells are situated near the stigmata and the main 

 lateral tracheae. (Kolbe.) 



According to Kowalevsky, the pericardial cells, and the garland-shaped, cellu- 

 lar cord consist of cells, whose function it is to purify the blood, and to remove 

 the foreign or injurious matters mingled with the blood. 



Ampulla-like blood circulation in 

 the head. In the head of the cock- 

 roach occurs, according to Pawlowa, 

 a contractile vascular sac at the base 

 of each antenna. The cavity has a 

 valvular communication with the 

 blood space below and in front of 

 the brain, and muscle-fibres effect 

 systole and diastole. Each sac is 

 beyond doubt an independently ac- 

 tivp nart of thp nirpulatnrv ssvstprn FIG. 379. Diagram of the circulatory organs in 



m ' the head of the cockroach, seen from above : A, am- 

 These organs also occur in Locusta pulla; V, antennal vessel; M, chief muscular cord; 



and othpr Aprvrliifl* ami Splva , muscular band ;&, wall of the blood sinus ; 

 atner Acrydiiclae, and belva- an ^ openlng of the aorta (a) . r(A antei . lor symi ,a- 



tico has described similar structures thetic or visceral ganglion ; hg, hinder visceral gaii- 



in itonbyx mori and certain other $?%: | ^ ia ^ LICSow^ ; 

 Lepidoptera. 



Pulsatile organs of the legs. Accessory to the circulation is a special system 

 of pulsatile organs in the three pairs of legs of Nepidre, generally situated in the 

 tibia just below its articulation with the femur, but in the fore legs of Ranatra, 

 in the clasp-joint or tarsus, just below its articulation with the tibia. First 

 observed by Behn (1835), Locy has studied the organ (Fig. 380) in Corixa, 

 Notonecta, Gerris, besides the NepidaB. It is a whip-like structure attached at 

 both ends, with fibres extending upward and backward to the integument of the 

 leg, separate from the muscular fibres and does not involve them in its motions, 

 and is not affected by the muscles themselves. "As the blood-corpuscles flow 

 near the pulsating body they move faster, and around the organ itself there is a 

 "whirlpool of motion." The beating of these organs aids the circulation in both 



