346 TRANSACTIONS LIVERPOOL BIOLOGICAL -SOCIETY. 



done on the subject. The following account agrees with 

 his results, except that in Gammarus pulea: the posterior 

 aorta divides into two branches instead of into three, as 

 he found to be the case in TaJitrus locusta, and that the 

 excretory organ breaks the continuity of the pericerebral 

 vascular ring. The facts given below have been drawn 

 from observation of the course of the corpuscles in the 

 living animal, checked, however, by the examination of 

 serial sections. 



The heart is a long wide tube (PL II., PL III., fig. 1, 

 Jit.) extending from the middle of the first segment to the 

 middle of the sixth, beyond which it is continued back- 

 wards as the median dorsal posterior aorta. In front, it 

 is continuous with the median dorsal anterior aorta. In 

 its anterior part, the ventral wall of the heart touches 

 the dorsal wall of the anterior diverticulum of the alimen- 

 tary canal, but further back it is separated from the gut 

 by connective tissue. The dorsal wall of the heart is 

 attached to the integument in the middle of each seg- 

 ment by a bundle of connective tissue fibres (PL III., 

 fig. 1., al. c.) ; these are the alse cordis, between which the 

 heart hangs freely, forming five arcades through which 

 the blood of the pericardial cavity can pass over the heart 

 from side to side. In the middle of each segment, the 

 lower part of the heart is widened by lateral fibres 

 attached to its walls and the pericardium, which draws 

 out the former laterally. In section, the wall of the heart 

 appears to be formed of thin connective tissue, supporting 

 somewhat scattered muscle fibres, which are most closely 

 packed round the ostia. The latter (PL III., fig. 1, os.) 

 are three pairs of obliquely-placed slit-like openings, 

 without valves, situated a little behind the middle of the 

 second, third and fourth segments. They open during 

 diastole, and their edges are drawn together by the 



