176 



BULLETIN OF THE BUREAU OF FISHERIES. 



In this table the entire length of the parasite, excluding the egg strings, is called 

 loo. The distance of each pair of legs from the anterior end is reduced to the proper 

 percentage of loo, so that a comparison of the figures one with another gives the actual 

 relative position of any pair of legs on any species. 



These relative distances are not claimed to be constant for any given species, but 

 probably vary within certain limits; such individual variations, however, are likely to 

 be considerably less than the specific variations given in the table. The gradual increase 

 in these distances from in front backward shows that in the final elongation of the body 

 after attachment to the host every free thorax segment has a share. 



The anterior segments are not elongated as much as the posterior, but each con- 

 tributes something. In the other genera of the Lenueidae the bunching of the legs just 

 behind the head shows that the great bulk of the elongation is contributed by the fifth 

 and sixth segments. 



Of the first four pairs of legs each is biramose and made up of a broad basal joint 

 and two slender three-jointed rami. On the iimer margin of the basal joint the first 

 legs carry a stout claw, the other three pairs a single plumose seta. There is a fifth pair 

 of legs just in front of the external openings of the oviducts; each leg is composed of a 

 single hand-shaped joint armed with setae. These legs do not get broken off in the 

 mature female as easily as in the other Lernaan genera, where they are all bunched 

 closely together. 



Claus first called attention to the fact that these swimming legs neither degenerate 

 nor disappear, contrary to the usually accepted understanding of the Lemseidae. There 

 is no diminution in size, in the number of rami or joints, or in the plumose setae with 

 which they are armed. The legs simply remain exactly as they were at the close of 

 the copepodid stages when the parasite sought out its final host. They do not develop 

 in accordance with the enormous increase in the size of the thorax and abdomen; but 

 neither do they lose anything, not even a single seta of their armature, and hence they 

 can not be said to degenerate. Similarly, the only disappearance is one due to breakage 

 consequent on the burrowing habits of the parasites, which is a very different thing 

 from degeneration. 



The swimming legs are situated in transverse shallow grooves which mark the divid- 

 ing lines between the thorax segments, the anterior slope of the groove being a little 

 higher than the posterior. Each pair of legs is joined across the median line by a trans- 

 verse rib, which hes just in front of the groove and is thoroughly fused with the body 

 wall. 



