14 Mr. C. S. Bate on the Morphology of some Amphipoda 



to some of the appendages. For instance, the third and fourth 

 pairs of pereiopoda in Vibilia are, in the adult, of the same 

 form, their most remarkable feature being that the propodos 

 is nearly one-half the length of the entire limb ; it is armed with 

 minute spines upon the anterior or flexible margin, and is capable 

 of being doubled back against the preceding portion of the limb, 

 being rendered more securely prehensile by the presence of two 

 lateral, short, stiff spines at the antero-distal extremity of the 

 carpus, between which the propodos closes against the carpus. 

 In the young, these same organs, while differing from those of the 

 parent, also differ from each other, but only in degree, so that a de- 

 scription of one will serve for both. The carpus is antero-distally 

 produced nearly to the entire length of the propodos — in the 

 third pair not so much as in the fourth ; the propodos is an- 

 teriorly concave, the antero-distal angles being anteriorly pro- 

 duced (one on each side of the dactylos) to a sharp point, — the 

 dactylos, closing between them, falling into the anterior concave 

 groove, its apex antagonizing with the extremity of the carpus, 

 and thus forming a tolerably perfect but complex chela. This 

 change is still more complete in the morphology of the fourth 

 pair of pereiopoda of Brachyscelus. In the adult the basos is 

 broad and large, the remaining joints lying reflected against the 

 basos being considerably the shorter ; in the young the basos 

 is long and narrow, consisting of but a normal portion of the 

 limb, whilst the propodos is large, with the antero-distal angle 

 produced to a considerable process, and forming a strong ramus 

 against which the moveable dactylos is capable of striking, — 

 thus forming a very perfect chela, and one assimilating to that 

 of the third pair of pereiopoda in the genus Phronima. In 

 Platyscelus the alteration is less striking, though still extremely 

 great. The fourth pair of pereiopoda differ from the third in 

 having the basos more largely developed ; the five distal joints, 

 which articulate near the centre of the basos, are scarcely one- 

 third of its length, it being so monstrously enlarged as to equal 

 the entire length of the pereion. In the young, the third and 

 fourth pairs of pereiopoda resemble each other, and bear a 

 moderate resemblance to those of the adult form of Brachyscelus ; 

 that is, they differ from those of the parent by the monstrous 

 development of the basos only. 



Observing that such considerable and eccentric changes occur 

 in the progress of the animals from the earliest form to that of 

 the adult, and knowing that the law among the Amphipoda, 

 even including the aberrant forms of Caprellte, is, that the nor- 

 mal progressive development is a variation of degree only, I am 

 induced to think that the unimpoverished type of these genera 

 is to be found nearer to the young than to the adult form, and 



