liv 



INTRODUCTION. 



Fig. p. 



unnecessary to follow out the minor distinctions in the 

 various brachyurous genera. It is sufficient to state that 

 the investigations of Mr. Couch confirm fully the views of 

 Thompson, by the establishment of a metamorphosis of 

 similar character, as regards the first change, in the large 

 edible crab, Cancer Pagurus, in Portunus, and in several 

 of the Uaiache and Leptopotliada;. There are some minor 

 differences in the structure and form of the first stage of 

 these as compared with that of Carcinus, but they do 

 not involve any important consideration. The curious 

 little larva of Pinnotheres I have figured at p. 125, after 

 Thompson, and as I have myself seen it. 



Amongst the oxyrhynchous forms there are some rather 

 curious deviations from the type above described, par- 

 ticularly in the absence, according to Mr. Couch's figures 

 in the genus Maia, of the dorsal and frontal spines ; but 

 these, as I understand Kathke's description, arc found 

 in the corresponding stage of the neighbouring genus 

 Hi/as; if this be so, it shows that the existence or 

 absence of these spines is of little importance. 



In the Anomoura we have elaborate descriptions of the 

 young stage of Pagiirnx, in the paper by Rathke already 

 referred to, and in one by Dr. Philippi, with a figure.* 



* Ann. of Nat. Hist. vol. vi. p. <)2, pi. iii. f. 7, 8. 



