56 



THE ROYAL SOCIETY OF CANADA 



same general form as in the earlier stage, the antennales being unira- 

 mous and the other two biramous, but the details of their structure 

 could not be made out. Between the antennae and antennules of 

 either side, a large epistome occupied the middle line and in front of this 

 was a band of deeply staining tissue, evidently the brain and optic 

 lobes, immediately in front of which, in the median line, was the 

 unpaired naupliar eye, while laterally on either side was a fairly 

 large compound eye, in which pigment was already abundantly present. 

 Posterior to the epistome was a darkly stained area broadening 

 rapidly posteriorly and probably representing the region in which the 

 remaining masticatory appendages will be formed, although at this 

 stage there is no trace of these structures, nor of the segments which 

 will be associated with them. 



Succeeding this region is a distinctly segmented portion of 

 the body, consisting altogether of nine segments. The first 

 six segments are of almost uniform width, 

 diminishing only slightly posteriorly, but 

 the last three diminish in width rather 

 rapidly. On each side of the median line a 

 series of deeply staining blocks of tissue can 

 be seen, apparently representing the nervous 

 system. These extend back to the seventh 

 segment, so that there are only seven pairs 

 of ganglia, the last two segments being ap- 

 parently destitute of these structures at 

 present. Lateral to the ganglionic chain in 

 each of the anterior six segments a papilla- 

 like structure could be seen on either side. 

 These are apparently rudimentary appendages 

 which in older examples were seen to have 

 developed into biramous structures. No in- 

 dications of limbs were to be observed in the 

 last three segments. 



Posteriorly to the segmented region was 

 an oblong portion, unsegmented, denticulate 

 on the sides and apparently with minute setae 

 arranged in more or less transverse rows. 

 Posteriorly this region terminates in about 

 still within the shell of five ( ?) moderate spines, of which the lateral 

 Stage II. ones are somewhat curved. 



Hansen arrived at the conclusion that the y larvae were the 

 young of an Apodous form by a process of exclusion, the larvae of one 

 •or more members of each of. the other Cirrhipedan groups being known 



Fig. 10. Hansen's y larva. 

 Stage HI. From stained 

 and mounted preparation 



