584 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



Similarly in those species in which the second maxillae are united 

 throughout their entire length these longitudinal muscles remain sepa- 

 rate and thus witness to the paired origin of the attachment organs. 



4. Muscles of the other api^endages. — The mandibles and first max- 

 illae are each supplied with the usual muscles. The one attached to 

 the base of the mandible {rm, fig. 3) is a powerful retractor, wliich not 

 only draws the mandible back into the proboscis tube but also turns 

 it sidewise, so that the toothed edge points ventrally. There may be 

 either one or two muscles connected with the base of the first maxillae, 



but the amount of mo- 

 tion they produce is very 

 slight. The maxillipeds 

 are provided with the 

 usual muscles found in 

 such two-jointed ap- 

 pendages, those design- 

 ed for the flexion of the 

 terminal claw being usu- 

 ally very powerful. The 

 muscles of the fu'st and 

 second antennae also 

 produce but httle mo- 

 tion: these appendages 

 are often very obscurely 

 jointed and the muscu- 

 lature then gives the 

 most reliable informa- 

 tion as to the number of 

 joints. In some genera 

 (Basanistes, etc.) the 

 second antemiae are ex- 

 ceptionally developed 

 and are furnished with 

 the musculature neces- 

 sary to enable them to function as organs of prehension. The mouth 

 tube is also furnished with muscles by means of which it can be 

 directed and held against the skin of the host or withdrawn at 

 pleasure. 



5. Special muscles. — In addition to the muscles already enumerated 

 there are others which serve specific purposes and which consequently 

 deserve particular notice. The first of these may be termed the circu- 

 latory muscles, since it is through their contraction and relaxation 

 that the meager circulation in these parasites is maintained. There 

 are three pairs of them, an anterior pair in the third thorax segment, a 

 median pair in the fourth segment, and a posterior pair in the fourth 



-CiRCULATOKr MUSCLES OF ACHTHERES AMBLOPLITIS. 



a, Anterior; m, median; p, posterior. 



