ECONOMIC RELATIONS, ANATOMY, AND UFE HISTORY OF GENUS LERNiEA. 1 79 



ing the weak currents in the fluid filling the body cavity, which constitute the only cir- 

 culation that the creature possesses. 



The muscles. — Although the body of these parasites is quite distinctly segmented, 

 there can be no movements of the segments one upon another, because there are no 

 muscles to produce such movements. Here there has been a positive degeneration, 

 and the system of body muscles which was present and operative in the copepodid larva 

 at the time it attached itself to its final host entirely disappears in the adult. 



The only muscles left are those connected with the head, the proboscis, the appen- 

 dages, the vulvae, and the anal papillae. In the head there are two dorsal extensors which 

 move the entire head from above downward, and thus hold it against the tissues of its 

 host, and two ventral retractors which lift it up again. Similar extensors and retrac- 

 tors are connected with the proboscis, the antennae, and the mouth parts. 



Each pair of swimming legs retains the strong muscles which they originally pos- 

 sessed in the copepodid stage, including those connecting the basal joints with the inner 

 walls of the body, those moving the respective joints of the rami, and those which 

 operate the various swimming setae. 



Even the fifth legs retain the rudimentary muscles, which are all that they ever 

 possessed. The muscles connected with the vulvae are similar to those found in other 

 copepod families, especially the Lernaeopodidae, and are the ones controlling the passage 

 of the eggs out into the external sacks. The muscles which move the anal laminae 

 radiate from the bases of the laminae to the surrounding walls of the abdomen. All 

 these muscles are distinctly striated and are made up of bundles of fibrillae'. 



The nervous system. — The copepodid larvae possess a normal crustacean nervous 

 system. (See fig. 62, pi. xiii.) How far is this system modified or changed in the 

 adult? This question has not been answered by any of the investigators who have 

 worked with the present genus, for they knew nothing of the larva, and the nerves of 

 the adult are easily overlooked. 



In the first place it is evident that the muscles we have just described must have 

 some nerve center to control their movements. This is especially true of those in the 

 head, which move the head itself, the antennae, and the mouth parts. The need of a 

 proper control of these muscles is even greater in the adult than in the larva, for they 

 are all concerned in procuring food, so essentially necessary for the rapid and com- 

 paratively enormous growth from the larva into the adult, and for the formation and 

 nourishment of the eggs after the creature has attained its maximum size. Accord- 

 ingly, we find in the head some very respectable remnants of the supra-oesophageal and 

 infra-oesophageal ganglia. (See fig. 7, pi. vii.) While the outer portions of these gan- 

 glia are frayed and indistinct, those portions nearest the oesophagus are well preserved, 

 their nuclei are distinct, and there are still commisures connecting them around the 

 CESophagus. A good optic nerve can be detected leading from the supraganglion to 

 the eye and others to the antennae and mandibles, while the infraganglion supplies the 

 remaining mouth parts. A distinct ventral cord can not be detected, either in longitu- 

 dinal or cross section, but both the reproductive and digestive organs must be con- 

 nected with a nerve center in order to perform their functions aright. In general, there- 

 fore, we may say that the nervous system has not developed in accordance with the 

 rest of the body. 



The oesophageal ganglia and their commisures have increased in size from the 

 copepodid stage, but the nervous elements in the adult are not as clearly defined or 



