of the Fishery Board for Scotland. 141 
The II., I1I., and ITV. Zoée 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 IV. Zoé respectively ; and from the IV. Zoéa the 
Megalops was obtained. This was the method adopted by Mortensen* 
in the case of Palemon Fabricii, and later by myself with Crangon 
vulgaris. 
The variation in size between Zoée of the same stage was also 
noticed in the case of the Zoée of Crangon. Gurney found the same 
difficulty in the case of the Zowe of Corystes cassivelawnus, especially in 
the second stage. He, however, came to the conclusion that there 
were only four Zoéa 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 
Zoek. 
A useful character for separating the different stages is the number 
of sets on the exopodite of the first or second maxillipede, but this is 
not constant. 
In the I. Zoéa there are 4 sete. 
” aie 9 Ped 6 19 
? LET. 29 Pr 8 ” 
29 BY. 99 ? 10 9 
Two cases of III. Zoéa were found which had only six sete. 
The pleopods afford a character by which the ITI. and IV. Zoée can 
be separated from one another, and also from the I. and IT. Zoée. 
In the I. and II. Zoée the pleopods do not project beyond the 
ventral line of the abdominal somites. In III. and IV. they do so. 
In III. the pleopods of the second to fifth somites are half the length of 
the abdominal somite ; in IV. they are as long as the somite. 
In III. and IV. the pereiopods are large; in the latter they are 
segmented. 
As to the length of the Zoéa period I have no data except that the 
Zoéa of the first stage which was hatched on May 15th moulted into 
the second Zoéa 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 Zoéa period does not probably exceed a month. 
Characters of the Megalops (Fig. 152) and Early Young Stages. 
THE MzcAtops 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 Zoéa, viz. very 
transparent, hyalin. 
The abdomen projects in line with the cephalothorax; 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 
perelopods 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 (Palemon Fabricii, Rtk.).” 
Copenhagen ; 1897 
