PA RASITIC CnPEPODS—CA LldTD-E— WILSOX. 535 



the period of incii]);ition is approxiniatel}' 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 x'alue can Ix' (h'aw n on liiis 

 point without nioi'e extended ol)servations. Eight weeks is r(M(uired 

 in (J(iJ((j)is t'apa.i\ and fi'om eight to ten weeks in Lfp'op/it/idrtifi 

 peetovdllx. 



Hence while the stage of development reached by the various indi- 

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

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

 given stage of development is moi'e likely to ))e found than at others. 

 Nearly all the chalimiis stages used in the present paper were ol)tained 

 from connnon tiounders caught l)etween the middle and th(^ last of 

 August at Casco Hay on the Maine coast. The s(>ason would be a 

 little earlier in the vicinity of Woods Hole. 



Again the whole of the end)rvos in the (^vr^y tubes of a given female 

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

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

 through successive moults, as the material re([uires very little sorting. 



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

 tically certain that the emljryos will issue ])efoi'e the mother's death. 

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

 limited. H" it is desired to rear the embrj'os females should be selectefl 

 whose egg tu])es have the deepest color, and an almost total failure 

 luay be simply due to the inuuature condition of the eggs and not to 

 the environment. 



Usually each Qgg ruptures separately, and the inclosing UKMulu'ane 

 of the egg tu])e splits opposite the ^:^gg^ allowing the nauplius to 

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

 and nearlv all the l)reaks are on one side, l)ut in spiti^ of this the empty 

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

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

 mother, wheii 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 tirst break the 

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

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



As soon as they are full}' free the nauplii swim to the surface and 

 toward the light. P^ach has the typical nauplius form, ovate or ellip- 

 tical in outine, strongly flattened dorso-ventrall}', and with three pairs 

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

 dibles (fig. 36). The bodj- is very simple and without segmentation, 

 being made up of a cellular exterior surrounding the general bodj^ 

 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. 



