x liv INTRODUCTION. 



coveiy, that even the Decapods, after they have already 

 quitted the egg, undergo a very considerable metamor- 

 phosis; 1 ' and, in conclusion, he adds, " from the notices 

 which I have here briefly communicated respecting the 

 development of some Decapods, it results that several of 

 these animals, as first discovered and described by Thomp- 

 son, undergo a very considerable and highly remarkable 



metamorphosis I, therefore, confess that I 



have done Thompson injustice in not putting faith in that 

 discovery." And he then states his intention " next 

 spring, partially to subject his researches on the cray-fish 

 to revision."* There is one apparent anomaly, however, 

 on which Mr. Westwood dwells with some plausible show 

 of reason, and on which it may be well to offer a few 

 remarks. 



Amongst the specimens of Crustacea, preserved in 

 spirits, which formed part of the collection of the late 

 Rev. Lansdown Guilding, and which came into my pos- 

 session after his death, was one of the abdomen of a 

 female land crab, Gecarcimis, to which were attached 

 numerous young, in their perfect form, and very similar, 

 excepting in size, to the parent. Here, then, was a case 

 in which, it may at once be granted, no external and 

 independent metamorphosis, at least, had taken place ; 

 and on this, with the other instances above alluded to, 

 Mr. Westwood founds his principal argument against the 

 doctrine enunciated by Mr. Thompson. But may not 

 this probably be an analogous phenomenon to that of the 

 land salamanders amongst the amphibia? And, as in 

 that instance, where the parent has no opportunity 



* Wiegmann's Archiv. part iii. 1840. Translated in Ann. Nat. Hist. vol. vi. 

 pp. 263-2GB. 



