APPENDIX III 



CIRCULATION 



As far as we know, since Zaddach's time no detailed 

 account of the circulation of Apus has been given. Ger- 

 staecker adopts and incorporates Zaddach's description in 

 Bronn's Klassen imd Ordnungen, vol. v. Zaddach's ob- 

 servations seem to have been made on living transparent 

 animals. All who have tried this method know how diffi- 

 cult it is to make out the details, however visible some of 

 the main streams may be. Thus Zaddach's plan of the 

 circulation requires considerable amendment. 



As already pointed out in the text, the system is a 

 lacunar system through which the blood is propelled by a 

 contractile dorsal vessel or heart. On the expansion of the 

 heart the blood is drawn out of the cardial sinus to be 

 propelled forwards through (i) the anterior aorta to supply 

 the head and liver, and (2) the two lateral vessels which 

 dip down under the shell gland to convey blood into the 

 shield. 



The heart is composed of striated circular muscle fibres 

 crossing each other diagonally — the muscle-cells being 

 turned inwards, and forming a kind of syncitial lining 

 to the tube. The heart is suspended by an exquisite 

 arrangement of connective-tissue fibres, which, seen together 

 under a low power, take the form of triangular wings. 

 These connective tissue alse are not flat and membranous, 



