26 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.B3. 



host and has begun her retrogressive metamorphosis the muscles 

 share in the changes produced. As the body fuses and becomes 

 swollen and tumid and the appendages cease to be used the muscles 

 also fuse and disappear until there is nothing left in the adult female 

 but a simple network between the integument and the alimentary 

 canal to be noted under the digestive system (p. 27). 



There are still the usual muscles connected with the antennae, 

 especially the second pair, with such of the mouth parts as are still 

 used, with the swimming legs of those genera in which they are bet- 

 ter preserved, and with the anal papillae in Lernaea, Penieulus, etc., 

 and in even the most retrogressive genera there are still muscles con- 

 nected v.'ith the external openings of the o^ iducts, which control the 

 passage of the eggs into the external sacks. But the other muscles, 

 including all those which flexed or moved the body of the copepodid 

 larva, entirely disappear. In Lernaeenicus the proboscis is highly 

 developed and possesses a complicated system of muscles whereby each 

 part of it, as well as the mouth parts connected with it, can be moved 

 independently. 



But the swimming legs are less well preserved and their muscula- 

 ture is correspondingly reduced. In Peniculus the jointed thorax 

 retains more or less of its capability of motion, and with this most 

 of the muscles. 



Tke alimentavy canal. — ^The mouth opens into a short esophagus, 

 which is usually straight or but slightly curved, and is inclined to 

 the axis of the head. It opens into the stomach on the ventral sur- 

 face of the latter, near or at the anterior end, and the opening is 

 guarded by a powerful sphincter muscle. In those genera {Ler- 

 tmeenicus, Penieidus^ etc.) in which there is a protrusible proboscis 

 the extension and retraction take place principally in the mouth 

 tube, and are shared only incidentally by the esophagus and at its 

 anterior end. The muscles, which control these movements, are at- 

 tached chiefly to the base of the mouth tube (fig. ()9) and draw it 

 in or push it out without affecting the esophagus very much. 



When the proboscis is protruded the stomach is drawn forward by 

 the muscles at its anterior end, and this shifts the position of the 

 esophagus and allows it to follow the movement of the mouth tube 

 without itself undergoing much change of length or diameter. Its 

 walls, however, are elastic and are probably stretched a little dur- 

 ing the extension of the proboscis and recover their normal form 

 when it is retracted. 



The stomach is abruptly enlarged behind the sphincter muscle 

 and is sometimes straight and sometimes convoluted. In the genus 

 Lernaea it also sends out a lobe on either side, but these lobes are 

 not connected in any way with the horns, nor can they be said to 

 enter the base of the horns, as Claus, Hartmann, and some others have 



