The oviduct has its orifice between the fourth pair of feet. The 

 receptacuU seminis are two dark-coloured, oval-shaped bodies situated 

 at the base of each lobe of the tail-plate, and, as their name implies, 

 are the receptacles for the male fertilising element (Fig. 12). Claus 

 says emphatically that there is no connection between them and the 

 ovary; that the female fertilises the ova as they pass from the oviduct, 

 by inserting in them the papilla conveying the male element. This 

 is more effectually accomplished by the upward motion of the tail- 

 plate during oviposition, and thus pressing the point of the papilla 

 into the egg. The papillae referred to are situated on the dorsal 

 side of the tail-plate immediately above each receptaculum, but a 

 little nearer to the orifice of the oviduct. They are minute pointed 

 hooks, which lie concealed within a pouch-like sac. They com- 

 municate with the receptaculi by means of delicate tubes. 



Physiological Functions. 



The circulatory system is in a rudimentary stage, so to speak. The 

 heart or dorsal vessel is situate in the last segment of the thorax, 

 immediately above the base of the tail-plate. Its pulsations take 

 place once every second, when the blood, containing small round 

 diaphanous globules, may readily be seen in circulation. The best 

 situations for observing this are in the outer margin of the tail-plate 

 and in the channels surrounding the paired eyes ; beyond these there 

 do not appear to be any definite vessels wherein the blood circulates. 



The brain and nervous system are connected with all the vital 

 organs of the body, the former being situated immediately above 

 the single eye. Thence proceed, by means of central ganglia, branches 

 to the paired eyes, antennae, suckers, foot-jaws, feet, and reproduc- 

 tory organs. 



The muscular system is well developed, particularly in the region 

 of the suckers and feet, where the striped muscle bundles may be 

 seen. There are several chitinous bands connected with the muscles, 

 which actuate the movement of the carapace and mouth organs. 

 There are also four oval-shaped chitin rings, two on either side of 

 the carapace. 



Concerning the respiratory system little is known. According to 

 Claus there is no satisfactory ground for supposing that there exists 

 a definite respiratory area ; that the constant motion of the swim- 

 ming-feet is probably connected with respiration, their structure 

 being similar to the branchiopoda and their use the same. Some 

 observers consider the tail-plate to be an organ of respiration. 



The alimentary system is somewhat complex. The main canal, or 

 stomach intestine, as it is called, commences at the base of the 

 mouth organs and occupies about one half of the thorax. It is then 

 joined by a smaller channel or intestine, which terminates at the 

 anal opening. The large intestine has two main branches on either 



