no. hoi. PARASITIC COPEPODS—CALIGIDJE— WILSON. 535 



the period of incubation is approximately the same for all members of 

 the same species. And so far as known it does not vary much in 

 different species, although no judgment of value can be drawn on this 

 point without more extended observations. Eight weeks is required 

 in CaMgus rapax, and from eight to ten weeks in Lepeopktheirus 

 pectoral '/.v. 



Hence while the stage of development reached b}^ the various indi- 

 viduals found on any given fish may be widely different they are just 

 as likely to correspond closely. And there are certain times when a 

 given stage of development is more likely to be found than at others. 

 Nearly all the chalimus stages used in the present paper were obtained 

 from common flounders caught between the middle and the last of 

 August at Casco Bay on the Maine coast. The season would be a 

 little earlier in the vicinity of Woods Hole. 



Again the whole of the embryos in the egg tubes of a given female 

 hatch at practically the same time, onty an hour or two between the 

 first and the last. This greatly facilitates the rearing of the embryos 

 through successive moults, as the material requires very little sorting. 



It' a female is captured with eggs nearly but not fully ripe it is prac- 

 tically certain that the embryos will issue before the mother's death. 

 Rut of course in such cases the percentage of survival is extremely 

 limited. If it is desired to rear the embryos females should be selected 

 whose egg tubes have the deepest color, and an almost total failure 

 may be simply due to the immature condition of the eggs and not to 

 the environment. 



Usually each egg ruptures separately > and the inclosing membrane 

 of the egg tube splits opposite the egg, allowing the nauplius to 

 wriggle out. There is thus a break in the tube for each of the eggs 

 and nearly all the breaks are on one side, but in spite of this the empty 

 cases are usually left still attached to the female after the last larva 

 has escaped. But sometimes, in the haste preceding the death of the 

 mot her. when there is scant time for the hatching, or when the eggs 

 lack considerably of being fully ripe, the result is very different. 



The struggles of the nauplii in freeing themselves first break the 

 tubes off from the genital segment of the mother and then tear them 

 all in pieces, leaving nothing but fragments scattered far and wide. 



A-> soon as they are fully free the nauplii swim to the surface and 

 toward the light. Each has the typical nauplius form, ovate or ellip- 

 tical in outine, strongly flattened dorso-ventrally, and with three pairs 

 of appendages representing the first and second antennae and the man- 

 dibles (tig. 36). The body is very simple and without segmentation, 

 being made up of a cellular exterior surrounding the general body 

 cavity, through the center of which passes the primitive digestive tube. 



The latter consists of a mouth opening on the ventral surface just 

 behind the bases of the first two pairs of appendages, and a straight 

 tube with no differentiation of parts. 



