A STUDY IN MORPHOLOGY. 



carefully examined and compared with fig. 43, and found to agree with it exactly. 

 It was then placed alone in a small beaker of sea-water. The next day it was found 

 to be moulting, and the drawing (fig. 50) was made from it immediately after the 

 completion of the moult. Other specimens, like fig. 50, were kept until they changed 

 their skins, and assumed a form a little larger than fig. 50, but similar to it in all 

 respects except that the abdominal appendages were now present as small buds. 

 Some of these were kept until they changed into larva) like the one which is shown, 

 less highly magnified, from the side, in fig. 54. The abdominal appendages were now 

 quite long, but still rudimentary, and the general form of the larva from above or 

 below, as well as the form, number, and arrangement of the thoracic appendages and 

 mouth parts, was like fig. 50. 



When seen from above or below (fig. 50) the carapace has nearly the same shape 

 that it had during the Zoea stages, but it now makes less than one-third of the 

 total length of the body, and a side view (fig. 54) shows that it is now only a little 

 deeper than the body, so that the basal joints of the thoracic limbs and maxillipeds 

 are exposed below its inferior border. The posterior dorsal spine and the two postero- 

 lateral spines have disappeared, and a pair of long antero-lateral spines (fig. 54, .s), 

 nearly half as long as the rostrum, have made their appearance underneath the eyes. 

 The rostrum (fig. 50, R) has the same shape and about the same relative length as 

 before, and the ocellus (Oc) is still present at its base. 



The compound eye (E) is mounted upon a movable stalk, which is quite short during 

 the first Schizopod stage, but it soon lengthens, as shown in fig. 55, which is a dorsal 

 view of the anterior end of the carapace of the larvoe shown in fig. 54. 



The first antenna has undergone more change at this than at all the previous 

 moults together. It is now about as long as the carapace, and each of the two long 

 cylindrical joints (fig. 50), which make up its basal portion, carries on its inner edge 

 three long slender two-jointed delicately plumose hairs. The base of the proximal 

 joint is swollen and carries a small hook-like process on its inner edge. The two 

 long sensory hairs have disappeared from the tip, which is unsegmented, pointed, and 

 ends in a bunch of short hairs. This appendage changes slightly with each moult, 

 and in the third Schizopod stage (fig. 54) the distal half of the proximal joint (fig. 56) 

 has separated from the proximal joint, so that the shaft is made up of three instead 

 of two portions. The hook is still present on the swollen base of the first joint, and 

 behind it the otocyst (e] has made its appearance. The terminal joint or flagellum has 

 now lengthened, and it carries three long sensory hairs which spring from about the 

 middle of its outer surface. 



The changes which the second pair of antenna undergo at this moult are even 

 greater than those which take place in the first pair. Their locomotor function is 

 lost ; the long swimming hairs have disappeared ; and in the first Schizopod stage 

 (fig. 50) the appendage is quite rudimentary, unjointed, less than one-half as long as 

 the first antenna, and divided into an exopodite and an endopodite which are nearly 



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