GENERAL ANATOMY. 19 



then passing througli lacunae scattered throughout the 

 tissues of the animal, and finding its way back to the 

 heart, which it enters by slits in the walls of that 

 organ. 



Reproduction. —The sexes in the Copepoda are always 

 separate, sexual differences showing themselves even 

 externally in the form and structure of the body ; in 

 some, especially in parasitic species, the dimorphism 

 is most remarkable, the male becoming little more 

 than a motionless sperm-sac attached to the body of 

 the female ; but in the species which come within the 

 scope of this memoir the males are usually smaller, 

 more active, and less numerous than the females, the 

 chief external distinctions being found in the almost 

 constant conversion of the anterior antennge — less 

 constantly of the fifth pair of feet, and occasionally 

 also of the posterior antennae and foot-jaws — into 

 clasping organs. The ovaries and testes are placed in 

 the middle or in the sides of the cephalothorax, com- 

 municate with accessory glands, and have efferent 

 canals, which open by distinct apertures on the sides 

 of the first (or conjoined first and second) abdominal 

 somites. The efferent canal of the ovary may be 

 simple, or may give of£ laterally a number of pouches, 

 which hold the eggs {Gorycasidce), while in some para- 

 sitic species it forms several terminal coils, in which the 

 eggs are detained; in the Notodelphyidce the duct is 

 converted into a large dorsal pouch or pseudo-uterus, 

 covered only by the integument, in which organs the 

 ova undergo partial development. In the free Cope- 

 poda, however, the ova pass at once into two (often coa- 



