14 BRITISH PARASITIC COPKPODA. 



ClUCULATORY SYSTKM. 



There is no heart in Lepeophtlieirus, nor are there 

 any proper blood-vessels. The circulation is wholly 

 laounar. The blood-streams simply pass through the 

 spaces left among the internal organs and between 

 the connective-tissue bands of the body-wall. The 

 streams appear to have certain definite courses, but 

 they are not uniform, continuous currents. The fluid 

 progresses by successive jerks, due to the peristaltic 

 movements of the alimentary canal. The blood is a 

 clear fluid containing numerous colourless corpuscles 

 which vary in size and shape. The corpuscles are 

 able to accommodate themselves to the diameter of the 

 spaces through w T hich they pass. There are no inde- 

 pendent organs of respiration, unless the pore-canals 

 and glands in the basal joint of the protopodite of the 

 second and third pairs of feet act as such. Hartog* 

 and others have suggested that the blood is probably 

 aerated from the sea- water contained in the alimentary 

 canal by the method of " anal respiration." Further 

 precise observations are, however, required to sub- 

 stantiate this hypothesis, as the method is so entirely 

 different from that in the higher Crustacea. 



MUSCULAR SYSTEM. 



The muscular system is a very complex one, as 

 shown by the illustrations of the dorsal and ventral 

 surfaces on Plate XIII. The members of the Cali- 

 goida as a general rule are so very transparent, 

 however, that the investigation of the musculature 

 can be carried out with very little effort. An excel- 

 lent description of the muscular system is given by 



* " The morphology of Cyclops and the relations of the Copepoda," ' Trans. 

 Linn. Soc. Lond.' (2), vol. v, pt. 1, pp. 1-46, 1888. 



