40 REPORT — 1877. 



poda, loses much of its original functional power. It may hold any 

 object, hut it cannot reach its mouth with it ; consequently we may 

 assume, finding it only in the male, that it is used chiefly as a weapon of 

 offence and defence. 



In the common Lobster (Homarus marinus) we find the same to a certain 

 extent, but not to such an exaggerated degree ; nor is it confined to the 

 male, only that the large chela is developed to so great an extent that it 

 cannot reach the mouth. In this case we have learned, from observation, 

 that the animal feeds itself with some of the posterior chelate appendages, 

 while it uses the first pair only for holding the food. 



It is not often that any of the posterior pairs of pereiopoda arc developed 

 into important chela?, but eveu this is the case in some genera. The most pos- 

 terior pair in which we arc aware of a largely developed chelate organ exists 

 in Stenopus among the Macrura, and Phronima an&Phrosina among the Amphi- 

 poda. In some genera, particularly among the Anomura, the two lust pairs 

 of pereiopoda are developed into small chelate organs. In Dorype they are 

 adapted for grasping any piece of wood, shell, or foreign body that the animal 

 may hold on its back sufficiently important to find protection under. In the 

 genus llomola the posterior only is so developed, tho penultimate resembling 

 those anterior to it. In Pagurus and Cenobitus they are developed into very 

 small chelate organs, and are used for very different purposes. 



One of the most important is to supply the place of a flabellum that is 

 wanting in the branchial chamber of this family. With this purpose the 

 animal passes it into the gill-cavity, and there cleanses and wipes the branchial 

 organs with the brush of hairs that is attached to it, or removes particles of 

 dirt or objects of detriment by means of the pincers. Moreover, it has the 

 power of feeding itself with these same organs under peculiar circumstances, 

 as related by Mr. Darwin in his ' Naturalist's Voyage.' 



lie tells us that some of these animals, as Birgus, live chiefly on the 

 land, that they frequently live on the cocoanuts which fall from the trees, 

 and that they first pidl off all the husk or rind from the outside, invariably 

 selecting the end where the eyelets are. These being exposed, they, 

 with their heavy claw, tap one repeatedly until they break it in; 

 then, inserting one of the posterior pairs of pcreiopoda into tho hole, they 

 draw up the juice of the cocoanut with the brush on the leg, and feed on 

 the milk — as singular and ivnusual an adaptation of means to an end as is 

 perhaps to bo found in the history of animal instinct, being one that is highly 

 suggestive of educational knowledge. 



\\ ncre the pereiopoda are developed for natatory purposes, they are gene- 

 rally of a more feeble and less perfect type. In the 8chizopoda they have 

 the character of weakened or impoverished appendages. The secondary parts 

 increase in importance, while the primary become depreciated. The 

 branchial organs lose much of their internal character as well as their high 

 structural features, while the hairs on the appendages and general surface 

 arc increased both in number and size. In fact tho rigidity of the leg is 

 lost, and tho flexile nature of a fin is acquired. This would appear as if 

 atavism, or a retrograde character, were apparent in the development of the 

 pereiopoda in the Schizopod group. 



In Nebalia and the Thyllopoda the general characteristics of the pereiopoda 

 partake more of a larval or embryonic form, bearing, as they do, a near re- 

 semblance in character and general appearance to the oral appendages in the 

 zoea of Crustacea than to any retrograde or impoverished condition. 



