fOLOGY. 



-cribe the heart of a cockroach 

 n chambers, corresponding to ten abdominal and 



three thoriu The clianibers of the heart arc .separated 



hich permit the blood to flow only towards the head. 

 There is in the walls of the heart a pair of lateral openings corre- 

 sponding to each chamber; th are furnished with val 

 which admit the blood to the heart, but prevent its exit. When, 

 therefore, the chambers contract, a stream of blood is forced towards 

 the head ; and when the}- expand, the blood rushes into them 



ral openi: 



The circulatory system has been careful!}' studied in only a few 

 : and these show a remarkable variation in the form and 

 arrangement of the openings and valves.* But the result 

 of their operation is the same in all. A diagram of a hori- 

 zontal section of the heart of a May-beetle, based on the 

 cription by Straus- Durckheim (Graber represents 

 it as more complicated) will - an illustration, 



represents a chamber of the heart during 

 it ile or contraction; the valves at the caudal 



-Dia- end and at the lateral openings (l) have been 

 !r\ of closed by the pressure of the blood; while the 

 valves at the cephalic end have been forced 

 and the blood, represented by the arrow, is flowing 

 . D represents a chamber regaining its natural 

 I the blood flowing into it through the lateral 



I have observed a somewhat different arrangement of 



1 valves in the nymph of a dragon-fly. A 



g individual was studied, one in which the skin was 



sufficiently transparent to allow the beating of the heart 



to be through it. In this insect the most active 



heart appeared to be the caudal chamber, 



wh: nted in . a. This chamber was in 



inding and contracting in rapid suc- 



With -..ansion the valves at I quickly closed and 



ed in at 2; and when the chamber contracted, the 

 1 and the blood \\ as forced forwards through J. 



* See Dr. V. Grabcr, Uebcr <lcn propulsatOfiscben Apparat <kr Insccten, Archiv ftir 

 mikroscopisrhc An.r 73). 



ix Artie ulcs (1828). 



