29 



The distinctly greater width between the bases of the last 

 pair of walking legs in the case of the female is therefore a 

 characteristic and easily-recognised feature, being 27 mm. in 

 the female as compared with 11 in the male of a crawfish 100 

 mm. in length of carapace. 



(6) Another marked difference between male and female 

 crawfish, though not recognised without closer examination, 

 is in the position of the genital openings, these being at the 

 base of the last pair of walking legs in the male, while they are 

 at the bases of the third pair in the female. 



(7) Finally, there is a well-marked structural feature in the 

 female not found in the male. This is a small pair of pincer- 

 Hke claws (chelae) found at the end of the fifth pair of walking 

 legs. These are not used for seizing prey, as is the case in the 

 large claws of the lobster, but are used for arranging, cleaning 

 and aerating the eggs. 



The points of external difference between male and female 

 are, therefore, numerous and well marked when analysed, 

 and although they may not be apparent to a casual observer, 

 are readily recognised by the experienced fishermen, so that, 

 though he may not be able to express these differences specifi- 

 cally, he can pick out readily enough the males from the 

 females in any lot of fish. 



6. Early Stages of the Crawfish. 



The various stages through which the crawfish passes after 

 hatching from the egg have been investigated at the Marine 

 Laboratory at St. James and by tow-nettings in and near 

 Table Bay. The eggs have hatched out satisfactorily and 

 some of the larval stages have been noted, while larvae of about 

 the same and older stages have been found in the sea. Three, 

 or perhaps four, more or less distinct stages have been noted 

 in all, but there are many gaps between these and the adult 

 form, and it will be the object of further investigation to find 

 these. On the results of such investigation will depend the 

 feasibihty of artificial hatching and rearing. 



The following short summary, however, may be given of 

 the results so far obtained. 



There emerges from the egg a small form entirely unlike the 

 adult.* Plate I shows the general appearance of the larva (en- 

 larged about 84 times) in the living condition. The body 

 is rounded or ovate and still contains some of the yellow 

 yolk granules of the egg stage. The antennae are at 

 this stage well developed. They have two branches and 

 these are provided with long projecting setae. By means 

 of thes e the animal swims about, rising first to the s urface of 



* A mrtie detailed description of this larval form has been published in the 

 loiirnal of the Linnit-an Society, London. 



[C.P. 5- I3-] 



