1 86 BULLETIN OF THE BUREAU OF FISHERIES. 



joint and two one-jointed rami, well armed with plumose setae and spines. The first 

 pair of legs is some distance in front of the posterior margin of the cephalothorax and 

 close to the bases of the maxillipeds. 



On the lateral margins of the second free joint near the posterior end are the rudi- 

 ments of a third pair of swimming legs in the shape of small papillae, each armed with 

 two set£. 



Total length, including anal setae, 0.53 mm. Carapace, 0.16 mm. long, 0.12 mm. 

 wide. 



Color a uniform yellowish white, digestive tube black, eye a reddish purple. 



When one of these larvae molts the old skin cracks open along the back of the thorax 

 and the larva crawls out through the hole thus made, just as a dragonfly or cicada 

 crawls out of its nymph case, and two minutes after emerging it is able to swim about 

 as before. 



Some molts occur without any change in the appendages or body segmentation 

 and with only a slight increase in the size of the larva. 



THE SECOND COPEPODID LARVA. 



Tn the second copepodid stage (fig. 21, pi. ix) obtained from the gills of the short- 

 nosed gar a new thorax segment has been formed just in front of the genital segment, 

 but the abdominal segments are still entirely fused. 



The first antennse have become four-jointed, while the second pair still remain 

 two-jointed. There are now three pairs of legs instead of two; the first two pairs 

 have two-jointed rami, while in the third pair the rami have but a single joint. The 

 new fourth segment carries at its posterior corners the rudiments of a fourth pair of legs, 

 each consisting of a large rounded papilla and two terminal setae. 



The second (first free) thorax segment has increased until it is fully as wide as 

 the cephalothorax, the third and fourth segments are about the same wndth, which is 

 two-thirds that of the second segment, and the abdomen has not increased at all. 



THE THIRD COPEPODID LARVA. 



The third stage (fig. 23-30, pi. ix) was obtained from the gills of thesauger, Stizostedion 

 canadense, and is evidently a different species from the one found upon the gar. But 

 it serves just as well to illustrate the changes which mark this stage. Another new 

 segment has been added to the free thorax, the second (first free) thorax segment still 

 remains as wide as the cephalothorax, while the other segments, including the genital 

 segment, diminish regularly in width behind it, though they are all about the same 

 length. The antennae are four-jointed and two-jointed, as before, but the second pair 

 has increased considerably in length. 



There are now four pairs of biramose legs, with the rami two-jointed, and a fifth 

 pair which is rudimentary, each leg made up of two papillae side by side and tipped 

 with short spines. There is also on either side of the genital segment at the posterior 

 comer a tiny papilla tipped vfith two small spines, the rudiment of a sixth leg. 



The abdomen has lengthened considerably and now has two joints, the basal joint 

 about half the length of the terminal one. There are also many differences in the anal 

 laminae and their setae, but these are probably specific differences rather than changes 

 due to advanced development. 



