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4. The "Puerulus" or "Natant 

 THE Cape Crawfish. 



Stage of 



This may be recognised by its very transparent, glassy body, 

 though otherwise superficially resembling a miniature crawfish. 

 The following is a preliminary note of this stage, details of which 

 will be published later. The body is not entirely colourless, 

 but has patches of the bright red colour seen in the earlier 

 stages iphyllosoma). These are very conspicuous on the 

 ventral side of the animal near the base of the legs, and on the 

 under side of the thorax. This colouring matter completely 

 disappears very soon after the animal is dead, and preserved 

 specimens retain it only for a few hours if exposed to light. 

 There are fewer spines on the shield, and the " swimmerets " 

 of the tail are well developed, each consisting of a relatively 

 large expodite and endopodite, the latter provided with a 

 coupling mechanism. These serve as swimming organs in 

 place of the outer branches of the walking legs, which have 

 now disappeared, leaving only rudiments or stumps in their 

 place. In the adults the " swimmerets " have never been 

 observed to function as swimming organs, being very much 

 reduced in the male, and converted into egg-bearing organs 

 in the female. The gills in the puerulus have become greatly 

 developed, and are now covered by the enlarged shield. The 

 change in the position of the gills is of interest. In the phyl- 

 losoma there are two on the upper side of the thorax (pleuro- 

 branchs), and one on the joint between the thorax and leg 

 (arthrobranch). In the adult there is one pleurobranch and 



[C.P. 6-'i4.] 



