64 



is much less active than the following stage, and that unless the 

 vessel containing the larvae is arranged so that there is a contmual 

 current sufficient to keep them suspended they will sink to the 

 bottom of the tank, and most probably be lost in any sand or 

 mud there, though, no doubt, there is a good deal of variation 

 in the length of time during which this stage maj^ persist. 



As regards the length of the first Zoea stage our observations 

 at Cullercoats are again divergent from Williamson's, but in the 

 opposite direction — that is to say, that while we find a longer 

 protozoea stage, the period during which our larvae remained 

 as first Zoeae is considerably shorter than his, viz., forty-eight 

 hours to seventy- two hours here, whilst he states that " Zoeae 

 of the first stage which hatched on May 15th moulted into the 

 second Zoea stage between the 24th and 27th, that is, after not 

 more than twelve days." This difference is interesting, as it 

 shows a considerable variation in the duration of the second stage 

 too, and, no doubt, the same is the case in the subsequent stages. 



In completing the series of figures of the later larval stages, 

 modifications of Williamson's^' and Faxon'sf figures have been 

 used, and an attempt made to indicate the relative size. William- 

 son gives us no actual measurements of the first four stages, but 

 takes the distance between the points of the dorsal and rostral 

 spines as the basis from which to indicate the relative sizes of these 

 stages in his drawings, but this gives no indication of the relation 

 between the size of the last Zoea and the Megalops, the size of 

 which he gives as 2-5 mm. broad and 2-7 mm. long (Brook'sJ 

 figures for this stage are much smaller, viz., '93 mm. and '43 mm.) 



My own measurements for the first three stages are as follows: — 



Protozoea ... ... 1'7 mm. long (average of seven specimens). 



First Zoea ... ... 1-95 mm. long (average of seven specimens). 



Second Zoea ... ... 2*1 mm. long (average of seven specimens). 



This shows an increase in size smaller than that suggested 

 by Williamson's drawings, but supposing the larvae to increase 

 at about the same rate in moulting into the third and fourth Zoea 

 stages, this fits in very well with the size given by him for the 

 Megalops, and it is on these figures that the relative sizes of my 

 drawings are based. The last two figures are taken from those 

 given by Brook. 



t " Bull. Mus. Compar. Zoology. Harvard," Vol. VI., p. 159. 

 t " Ann. and Mag. Nat. Hist," S. 5, Vol. 14, p. 202. 



