ON OUR PRESENT KNOWLEDGE OF THE CRUSTACEA. 91 



first two pairs of appendages are functionally utilized as attendants upon the 

 mouth]; and where this is not the case they are formed as organs of prehen- 

 sion, more especially among the male animals. This is exemplified even in 

 those species, as among the terrestrial Isopods, where the outward form is 

 less striking, but tlie whole appendage is strengthened for grasping piirposes. 



The next or ninth pair of appendages is almost if not universally formed 

 upon the same type as the preceding. There is a departvire in degree to bo 

 found, more pronounced in the Brachyura, in consequence of the appendages 

 crowding so much on one another. Thus, while those that experience most 

 the pressure of those that overlap them are precluded from attaining their 

 fully developed forms, the external ones, or they that overlap the preceding, 

 have, in order the more perfectly to fulfil their duties, extended their own 

 surfaces, so as more effectually to protect the oral cavity, as an operculum 

 covering the month. 



These two pairs are variated so constantly from the other appendages 

 of the percion that I think it will be foiind convenient in most cases to 

 designate them by distinguishing names. The licporter has, in the Eeport 

 on the Amphipoda in 1865 and elsewhere, called them gnathopoda, as feet 

 or appendages connected with the mouth ; and I see every reason whj' this 

 name should be adopted throughout the whole subkingdom, as one better 

 adapted, both functionally and homologically, than those proposed either by 

 Milne-Edwards's latest nomenclature, or the still less correct ones in popular 

 use of previous authors. 



In the larval form the second gnathopod is less advanced than the first, 

 but in the adult stage it is larger and more efficient. An exception to this 

 exists in Nehalia, where all the appendages of the pereion are developed 

 upon an immature or embryonic type. These gradually decrease in power 

 and form the more they recede posteriorly. All these appendages exhibit 

 the seven joints that are present in the formation of a single limb ; and in 

 those instances where there is a decrease in that number, the joint that is 

 wanting is lost at the extremity. This appears to be very general through 

 aU the Brachyural and Macrural divisions. 



In the higher forms both pairs of gnathopoda carry a secondary branch 

 as well as another that has generally been known as the " fiabelliform 

 appenage." For these Milne-Edwards has proposed the name of endognathe 

 for the primary or internal ramus, exognathe for the external or second 

 ramus, and epignatJie for that which is generally known as the " fiabelliform 

 appendage," and mesognathe for the fourth. But as the representatives or 

 homotypes of these same appendages occur in different grades of Crustacean 

 form, and whenever they do occur they bear the same relation to the limb 

 from which they spring, it would be better that they should consistently 

 be known by their homotypical character, rather than vary their name with 

 every succeeding appendage. Thus the fiabelliform appendage invariably 

 springs from the coxa or first joint, and is homotypical of the branchial 

 organs in other pairs of limbs ; another is invariably connected with 

 the hasos or second joint, and the third has its origin in the ischium or 

 third joint. One or all may be suppressed ; but whenever either the 

 one or the other is present it has its origin in its own peculiar joint, 

 and as such should be identified in any scientific nomenclature. I there- 

 fore suggest the names of coxecjjJii/sis, hasecphysis, and iscliiecpliysis for the 

 several parts*, as branches springing fi'om those joints, in whatever appen- 

 dage they may be found. Thus the secondary branch that exists attached to 

 the legs in Phyllosoma or the yoimg of Palinurus is an ischiecphysis ; in 



* The name of the joint being compounded with the word eKipvais, sprout or branch. 



