of the Fishery Board for Scotland. 



141 



The II., III., and lY. Zoea? obtained from the latter source were kept 

 until they moulted, and the resulting stage was in the case of the first 

 two the III. and lY. Zoese respectively ; and from the lY. Zoea the 

 Megalops was obtained. This was the method adopted by Mortensen* 

 in the case of Palcemon Fahricii, and later by myself with Crangon 

 mdgaris. 



The variation in size between Zoese of the same stage was also 

 noticed in the case of the Zoese of Crangon. Gurney found the same 

 difficulty in the case of the Zoe^e of Corystes cassivelaunus, especially in 

 the second stage. He, however, came to the conclusion that there 

 were only four Zoea stages. 



The four stages are fairly widely separated by their sizes. Naked- 

 eye drawings are shown alongside Figs. 159, 148, 147, and 146. They are 

 intended to give a fairly accurate idea of the absolute sizes of the four 

 Zoese. 



A useful character for separating the diflferent stages is the number 

 of setae on the exopodite of the first or second maxillipede, but this is 

 not constant. 



In the I. Zoea there are 4 setae. 



J? III. ,, 8 ,, 



>) lY. ,, 10 



Two cases of III. Zoea were found which had only six setae. 



The pleopods afford a character by which the III. and lY. Zoeae can 

 be separated from one another, and also from the I. and II. Zoeae. 



In the I. and II. Zoeae the pleopods do not project beyond the 

 ventral line of the abdominal somites. In III. and lY. they do so. 

 In III. the pleopods of the second to fifth somites are half the length of 

 the abdominal somite ; in lY. they are as long as the somite. 



In III. and lY. the pereiopods are large ; in the latter they are 

 segmented. 



As to the length of the Zoea period I have no data except that the 

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

 the second Zoea between the 24th and 27th of the same month, that is 

 after an interval of not more than twelve days. From this it may be 

 fairly inferred that the Zoea period does not probably exceed a month. 



Characters of the Megalops ( Fig. 152 ) and Early Young Stages. 



The Megalops oan be readily distinguished from the Megalops of 

 other species. It has to the naked eye a dirty-greenish or olive 

 colouration. Microscopic examination shows the presence of a large 

 black chromatophore on the dorsum, and also that there is no dorsal 

 spine on the carapace. The intensity of the pigment varies. 



Its integument is similar in character to that of the Zoea, viz. very 

 transparent, hyalin. 



The abdomen projects in line with the cephalothoi-ax ; it has five 

 pairs of functional pleopods. 



On the basi-ischiopodite of the chela there is a large hook. 



The dactylopodites and propodites of the second, third, and fourth 

 pereiopods have small serrated thorns. 



On the dactylopodite of the fifth pereiopod there are three long 

 curved spines. 



There is a short rostral spine. 



* Mortensen, " Undersogelser over Vor Almindelige Rejes {Palcemon Fahricii, Rtk.)." 

 Copenhagen ; 1897 



