IMERICAN PARASITIC ARG ULIDuE— WILSON. 691 



network of longitudinal muscles around and over the cloaca which 

 keeps up a rhythmic contraction that greatly assists circulation. 



These have already been mentioned as one of the chief agents in 

 the larval circulation prior to the development of the heart, and they 

 seem to retain their function in the adult. 



Besjnration has been already fully discussed in the larva, and there 

 is nothing to be added here. It may be well to repeat that respira- 

 tion is integumental, and that it is not confined exclusively to the 

 abdomen. The lobes of the carapace have a respiratory function as 

 important as that of the abdomen, and become the chief centers for 

 blood purification in those species {catostomi^ etc.) whose abdomen is 

 comparatively very small. 



The nervous system is well developed, and consists of a dorsal l)rain 

 connected with a ventral chain of ganglia, and nerves running to the 

 various appendages. The brain consists of two portions, each of 

 which is lobed (fig. 20). The upper part is situated just beneath the 

 skin on the dorsal midline of the carapace, right over the common base 

 of the mouth and sting. Its three lobes have an outline and arrange- 



Fig. 19.— Side view of the heart of Argulus americanus (diagrammatic). (For lettering 



SEE Fig. 18.) 



ment similar to that of the parts of a clover leaf. The outer rounded 

 portions are almost transparent, but the inner borders, where the 

 three come in contact, are heavily pigmented, and show through very 

 prominently as a dark brown, almost ))lack, triangular spot. The 

 under part is much larger than the upper, is more oval or elliptical in 

 shape, and extends some distance in front of the pigment spot. It is 

 divided along its longitudinal or antero-posterior diameter into two 

 lobes, each of which passes insensibly at the anterior end into a thick 

 nerve running to the eye on that side. In most species these optic 

 nerves have a good-sized swelling, the optic ganglion, on their outer 

 borders just before reaching the eyes. 



The posterior ends of the lobes also pass insensibly into thick-set 

 commisures, which curve around the oesophagus on either side and 

 connect with the interior ventral ganglion*. 



At the point where they leave the lobes there is a considerable 

 swelling, the ''''schlimdgcmgUon^'' (Claus). From this swelling a nerve 

 runs forward to the posterior antenna?. There is also another nerve 

 leading to the anterior antenna? from some portion of this ventral 

 part of the brain, but I have been unable to locate it any more exactly 

 than Claus. 



