516 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvm. 



around inward and meet on the median line beneath the intestine. 

 The general course of these main currents is the same, but the details 

 differ greatly. As Pickering and Dana well say, they "are merely 

 main directions, and the blood flows into them or from them through 

 all their extent." The points where the main currents break up into 

 smaller currents and the courses of the latter also vary greatly. Pick- 

 ering and Dana describe in Caligus curtus two points upon the median 

 line where there is a valvular action, functioning somewhat as a heart 

 in this circulation. 



One of these is situated at the apex of the posterior thoracic joint; 

 there are here three valves, one in the center ventrally and one on 

 either side dorsally, the dorsal and ventral valves opening alternately. 

 The pulsations are regular, and from 30 to 10 a minute. The second 

 point is between the basal joints of the second antennae. (Pickering and 

 Dana call them the first maxillipeds.) Here there is a single membra- 

 nous valve playing back and forth and thus preventing the return of 

 the blood that has passed it in either direction. . 



It must not be inferred that these two descriptions are characteristic 

 of the two genera and that Caligus species have the valves while 

 Lepeophtheirus species do not. This would not be true; the descrip- 

 tions merely serve to indicate the amount of diversity to be found in 

 the details of circulation. 



After examining a larger number of species while alive it may be 

 found advantageous to publish these details in a future paper. 



RESPIRATION. 



There are no independent organs of respiration, but Hartog, in 1880, 

 described the anal respiration in Cyclops, Canthoca?nptus, and allied 

 genera, and suggested that the blood of these parasites may be aerated 

 in the same wa}^. That this is the actual condition the present author 

 has proved in several instances. And first, as noted by A. Scott (1901, 

 p. 21), the chitin exoskeleton is so thick over nearly all the body that 

 very little aeration could be effected through it, while the endoderm 

 lining the rectum is thin enough for this purpose. 



Then there are the necessary muscles for such respiration, dilators 

 running from the abdomen wall to the rectum, while the peristaltic 

 movements, common to the rectum as to the rest of the alimentary 

 canal, serve for the contraction. These dilator muscles are figured by 

 Claus (1861) for Lepeophtheirus thompsoni (which he calls Caligus 

 oranchidlis) in Plate XXXIII, fig. 5 of his memoir. They are said to 

 be present in Lepeophtheirus pectoral-is by A. Scott (1901, p. 21), and 

 they have been observed by the present author in Lepeophtheirus 

 edwardsi and in Caligus rapax (fig. 23) and C. oonito. These facts 

 create a strong presumption in favor of the existence of such respira- 

 tion, and it was only left to actuall} 7 observe it in the living animal. 



