314 MR. WESTWOOD ON THE SUPPOSED EXISTENCE 



or larva of the common or edible Crab," (PL VIII. fig. 1 .) " the disparity in size 

 is shown between a Zoe newly hatched and one which has attained its full deve- 

 lopment, and the changes which the various parts undergo during the growth of the 

 animal," (No. 2. Addendum,) as in the total absence of subabdominal fins, and in the 

 natatory division of the two pairs of feet having only four plumose setae in the younger 

 animal : and in a former passage he observes, that " the larger specimens may be 

 supposed to differ from such as occur of smaller size in the greater degree of deve- 

 lopment of all its parts ; thus, the eyes are more distinctly pedunculate, the natatory 

 division of the feet have an increased number of plumose setae, the rudiments of the 

 subabdominal fins are quite obvious, and the mandibles show the rudiment of a 

 palp : in other respects they are essentially the same." (p. 10.) 



In the second place, our author states that he had succeeded in hatching the ova 

 of the common Crab {Cancer Pagurus), which presented exactly the appearance of 

 Zoea Taurus, with the addition of lateral spines to the corselet. And in the addenda 

 to his second number he has again stated this circumstance, adding somewhat more 

 precisely, that he had protected a female Crab with spawn apparently ready to hatch 

 until the young burst from their envelopes and swam about in myriads under the 

 exact form of Zoea represented in the Plate. 



In the third place, Mr. Thompson has stated that the common Lobster undergoes 

 metamorphosis, " but less in degree " than any of the other genera in which he states 

 that he had observed this to take place, and " consisting in a change from a cheliferous 

 Schizopode to a Decapode, in its first stage being what I call a modified Zoe, with a 

 frontal spine, a spatulate tail, and wanting subabdominal fins, in short, such an animal 

 as would never be considered what it really is, were it not obtained by hatching the 

 spawn of the Lobster*." 



The only figure which accompanies this remark is given in tab. xv. fig. 13. of the 

 same work, of " the cheliferous member of the larva of the Lobster, in which a is the 

 claw ; b, the outer division of the limb, or future Jlagrum ; and c, the rudimentary 

 ' branchia." In this figure, three organs are represented as arising from a large basal 

 joint : first, the chelate organ, composed of two joints and a large didactyle chela ; 

 second, a three-jointed organ, of which the terminal joint is long, slender, and 

 strongly setose ; and third, a small rudimental branchia. 



In the fourth place, " this curious piece of economy," according to Mr. Thompson, 

 " explains what has ever appeared paradoxical to naturalists, viz. the annual pere- 

 grinations of the land Crabs to the sea-side, which, although acknowledged to be true 

 by several competent observers, could never before be satisfactorily accounted for." 

 (p. 9.) And again, in the Addenda to his second number : " Hitherto the rationale of 

 this long and dangerous journey did not appear ; naturalists have thought it strange 

 that an animal entirely terrestrial should not spawn in its native haunts, and rear its 

 young at home, instead of putting them to the trouble of a tedious and unknown 



* Zoological Journal, No. xix. p. 383. 



