560 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.55. 



separated, two lateral dorsal bands, one on each side, and four median 

 ventral bands. In the other genera there are four median dorsal 

 bands, separated a little along the midline, and four median ventral 

 bands. 



In Paeon all these muscles show distinct breaks at the dividing 

 lines between the body segments and enable us to determine what part 

 each segment has taken in the body elongation. A similar break in 

 the median dorsal muscles just before reaching the base of the anal 

 laminae shows that an abdomen is really present, even though it be 

 reduced almost to nothing and so thoroughly fused with the genital 

 segment as to be otherwise indistinguishable. The posterior processes 

 in the young Sphyrion (fig. 20) are manifestly attached to the abdo- 

 men. The base of the posterior processes in Paeon being posterior 

 to the muscle break, they must also be regarded as abdominal. 



The Fecond set of muscles, which are dorso-ventral, have no counter- 

 part in any of the other copepod families. They consist of indivi- 

 dual muscle strands either scattered uniformly over the 'entire area 

 between the intestine and the lateral walls of the trunk {Paeon^ Sphy- 

 rion), or gathered into bundles in restricted areas {Pehelula, Per- 

 iplexis). When scattered the individual strands are not usually 

 vertical, but are inclined a little in one direction or another. Between 

 these strands are woven the coils of the oviducts and by their contrac- 

 tion the muscles undoubtedly aid the passage of the eggs along the 

 oviducts. A simultaneous contraction of all the muscles produces a 

 depression of the dorsal and ventral surfaces of the trunk over the 

 area covered by the muscles. In the case of the restricted areas 

 such contraction produces pits symmetrically arranged and cor- 

 responding in position on the dorsal and ventral surfaces. There are 

 the usual muscles connected with the vulvae and assisting in the ex- 

 trusion of the eggs into the egg strings. 



Muscular system of the male. — The musculature of the male is 

 well shown in figure 59, which is a side view of the male of Paeon 

 ferox. The muscles of the cephalothorax are connected entirely with 

 the antennae and mouth parts, and every appendage except the first 

 maxillae is well supplied. The muscles of the second maxillae and 

 maxillipeds are especially numerous and powerful and must make of 

 those appendages very efficient prehensile organs. In the thorax 

 there are simply the usual muscles between the segm.ents on the 

 dorsal and ventral surfaces, which produce flexion and extension. In 

 the fused posterior portion, or trunk, there is in addition a strong 

 diagonal muscle on either side which aids in extruding the spermato- 

 phores. 



Alimentary canal.— The mouth opens into a short esophagus, 

 which is usually inclined dorsally and fairly straight, but in Rehe- 



