74 



two arthrobranchs, just the reverse of the condition shown in. 

 the phyllosoma. In the pueruhis there are three, which may- 

 be said to occur on the side of the body, and later stages show 

 that a new and enlarged joint is found, on which the two lower 

 gills are situated, while the third becomes surrounded by the 

 calcareous material, which is deposited on the side of the 

 thorax and separates it well from the other two. The puerulus is 

 quite devoid of calcareous deposits. The dimensions and 

 proportions of the body are of interest. The smallest puerulus 

 is very much smaller than the largest phyllosoma, and the 

 largest is larger than the smallest stage at which the adult 

 colouring and calcareous deposits occur — for convenience, this 

 might be called the calcareous stage. The length of the 

 carapace, in proportion to the total length of the animal, 

 becomes greater throughout the various stages, and this is 

 continued even through successive calcareous stages. 



The stages through which the Cape crawfish passes after 

 hatching are, therefore, as follows : — 



1. The naupliosoma, in which the antennae are biramous 



locomotory appendages, provided with long swimming 

 setae, the other appendages being relatively short 

 and devoid of swimming setae. 



2. The phyllosoma, in which the antennae become unira- 



mous and lose their swimming setae, the other 

 appendages becoming suddenly relatively elongated, 

 and the outer branch of the walking legs develop- 

 ing swimming setae. 



3. The puerulus, in which the antennules are relatively 



smaller the antennae large and uniramous. The 

 pleopods are biramous and act as swimming organs. 

 There are only a few spines on the carapace. 



4. The calcareous stage, in which deposits of carbonate of 



lime appear in the cuticle. The pleopods become 

 reduced, and lose their swimming functions. 



The complete life history of the Cape crawfish is not, how- 

 ever, yet known, there being several gaps in the series of 

 specimens procured. Thus, no stages have been found between 

 the phyllosoma of 3 -8 mm. in length and those of 24 mm. 

 From this the series is fairly complete up to 37 mm. 



The largest gap, however, is between the oldest phyllosoma 

 and the puerulus. Whether or not the puerulus with its 

 much-shortened body and legs, its curved shield, etc., at a 

 single moult assumes these characteristics, is as yet unknown. 



