24 



Dates of casting of sliell in four females from Saldanha Bay 



A. 



( 8th April 



1908 29th May. 



f 28th May. 

 ^9^9 -) 2ist October. 



( 27th May. 

 ^9^0 "i nth August. 



1911 8th July. 



The question as to how often crawfish cast their shell has not 

 yet been investigated. Judging from the analogy of the 

 European lobster, whose life history is now well known, this 

 would occur several times a year in the young and, as a rule, 

 once a year in the adults. In the above table we note that 

 A (90 mm. in length of carapace) cast its shell twice a year 

 with the exception of two years (1908 and 1911) ; C (104 mm. 

 in length and presumably older) cast its shell only once a 

 year throughout the five years, and at very regular intervals, 

 with the exception of the first (1907). 



The time of casting of the shell is mostly in the month of 

 June, but may be from April to October. This last date was 

 observed in the case of A in 1909, and is probably very excep- 

 tional, and perhaps connected with the fact that in this year 

 there was no spawning. 



The time of spawning — that is, the time of the extrusion 

 of the eggs from the body — was, as a rule, some days after the 

 casting of the shell. In cases in which the shell was cast 

 twice in the year it was after the second casting. In these 

 ■cases also it is noted that the spawning season is later. Thus 

 in specimen A, in which the shell was shed twice a year, 

 spawning took place in July and August (20th July, 1907 ; 

 6th July, 1908 ; 26th August, 1910), while in specimen C, 

 which only moulted once a year, spawning took place in June 

 as a rule (15th June, 1907 ; 23rd June, 1908 ; 28th June, 

 1910 ; nth July, 1911). Specimen C was older than A, and 

 it may be concluded, as far at least at these two cases are 

 concerned, that spawning is later in the younger specimen. 



With regard to the frequency of spawning, this appears to 

 be not more than once a year, and this M-as so even in the case 

 in which the shell was cast twice in the year, nameh^, after 

 the sec\nd moult. It has for long been a disputed point as 



