422 Mr. R. Gurney on the 



itself to open at the base of the second antenna. The anus 

 is still imperforate. 



The Third Nauplius. (PI. XII. fig. 4.) 



Seven days after the nauplii had entered the second stage 

 some were found to have moulted into a third stage and to 

 measure about '17 mm. In this stage the first three pairs 

 of appendages are practically unchanged, but a fourth pair is 

 now present in the form of simple cylindrical processes with 

 a single apical seta. These appendages may represent the 

 second pair of maxilla?. The anus still appears to be. im- 

 perforate. The blue colour surrounding the gut is now, and 

 remains in later stages, a distinctive and easily recognized 

 character. The maxillary gland is first seen at this stage. 



Later Nauplii. 



After the stage described above all my nauplii died off 

 with the exception of one individual which, one month after 

 hatching, had reached a size of "25 mm., but had no more 

 appendages than before. In this stage the first antenna? 

 have numerous setae and are distinctly three-jointed (PI. XII. 

 fig. 5). The second antenna differs from the preceding stage 

 in having two basal masticatory hooks instead of one, while 

 the mandible has lost the characteristic flat aesthete of the inner 

 ramus. At some distance behind the mandible is a fourth 

 appendage in the form of a bilobed plate bearing six setae. 

 Immediately behind this appendage a line is seen across the 

 body which marks the division between thorax and abdomen, 

 so that this appendage is evidently the second maxilla, and 

 not a thoracic appendage. I have not been able to find any 

 trace of a first maxilla. Further back the first pair of 

 swimming-legs can be faintly seen beneath the skin in some 

 specimens. 



I have not found any nauplii either larger than the one 

 here described or with any additional appendages, so that it 

 seems probable that this, the fourth, Nauplius stage changes 

 directly into the first Cyclopid stage. 



Cyclopid Stages. 



Between the last nauplius found and the free-swimming 

 adult condition I distinguish five stages, probably corre- 

 sponding to as many moults. As figures are given of these 

 stages, it is only necessary to add a short summary of the 

 changes that characterize them. 



