NO. 1788. NORTH AMERICAN ERGASILID^— WILSON. 289 



terior muscles the first Xc) runs from the posterior liorn of tlie T bacls:- 

 ward and outward to the posterior corner of the segment. Tlie other 

 three muscles are attached to the end of the posterior arm of the V and 

 run backward and inward side by side to the posterior margin of the 

 segment. The working of these muscles to control the genital open- 

 ings is simple ; when muscles a and c contract the two arms of the V 

 are pulled together and the opening is closed. When h and d contract 

 the two arms are pulled apart and the opening is widened (fig. 12). 

 In this manner the passage of the eggs out^vard into the external 

 sacks is controlled. 



If this muscular system be compared with that found in theCaligidse, 

 several conclusions may be drawn from the differences noted. 



1. The lack of dorsal grooves on the carapace in the Ergasilidse is 

 emphasized by the entire absence of those internal muscles which in 

 the Caligida; produced more or less flexion between the different areas. 

 There the carapace was made up of definite areas put together in such 

 a way as to allow some motion between them. Here it is just as 

 definitely one solid piece, with no possibility of motion between the 

 various parts. 



2. The fusion between the three anterior thoracic segments and the 

 head in the Caligida3 is not as complete as is the fusion between the 

 hrst segment and the head here in the Ergasilidse. There the flexor 

 muscles all stopped at the groove separating the head and first seg- 

 ment; here they all run past that groove without being changed in 

 the least. 



3. These facts magnify the value of the ability possessed by the 

 Caligidse to arch or depress the carapace and thus make of it an organ 

 of prehension in the form of a large sucking disk. The subfamily 

 Ergasilinoe can not use the carapace in this way at all. To compen- 

 sate for this loss, witness the grouping of large and powerful muscles 

 in the dorsal portion of the cephalon to control the enlarged second 

 antennae. These form a notable contrast to the comparatively weak 

 set found in corresponding position in the Caligidae. 



4. The grouping of powerful locomotor muscles over the second 

 and third legs in the Caligidse show that these two pairs are the chief 

 organs of propulsion. Here the locomotor muscles are distributed 

 equall}^ to the first four pairs of legs. Hence the latter must share 

 equally in the propulsion of the copepod. 



THE CCELOM AND ITS CONNECTIVE AND MUSCULAR TISSUES. 



The connective tissues within the coelom loosely fill the entire 

 cavity, leaving numerous irregular and scattered lacunae. Being con- 

 nected with the integument of the body wall, as well as with that 

 which covers the various internal organs, they act as mesenteries to 

 support the alimentary canal and reproductive organs (fig. 15), 



Proc.N.M.vol.39— 10 21 



