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



nent or adult features present, but in an imperfect state, the 

 process of development being as yet incomplete ; and, as I ob- 

 served in the " Report on the British Edriophthalma," in the 

 British Association Reports for 1855, p. 55, "Although the re- 

 semblance to the parent is very considerable, yet it is by no 

 means complete; and it is probable that several moults are 

 undergone before the perfect development of the animal is ma- 

 tured." And, arguing from this datum only, we could subscribe 

 to Milne-Edwards' s theory, that the condition of the young ani- 

 mal first exhibits the form of the family to which it belongs, 

 next the genus, and lastly it betrays the species from which it 

 sprang. But this doctrine appears to be at variance with the 

 character of development in the present division, unless we are 

 to assume that the type of the family is to be found in the genus 

 Oxycephalic, and not in Hyperia. 



The young animal, when it quits the ovum, does not leave it in 

 a larval condition, but assumes the form consistent with the cha- 

 racters of an adult animal ; that is, its permanent organs are not 

 in an embryonic or larval condition, as is the case with the Zoe of 

 the Decapoda, but are present in a more or less perfectly developed 

 state. Thus, the anterior antenna? in Vibilia exhibit a character 

 in the young animal more consistent with the normal condition 

 of these organs than is to be found in the adult, while the reverse 

 is to be seen in the posterior antennae. The gnathopoda appear, 

 in the young animal, to exhibit features of an immature condition ; 

 whilst the pereiopoda, with the exception of the fifth pair, exhi- 

 bit the condition of fully-developed organs. That they differ 

 from those of the adult is true ; but, with the exception of a 

 distinction in form, those of the young appear to be as efficiently 

 developed organs as those of the parent. The fifth pair of pereio- 

 poda, in the young, have not assumed the complete form of the 

 parent ; neither have the appendages attached to the pleon. As 

 in Vibilia, so in Platyscelus, we find some parts of the animal 

 more advanced in the young stage than in the adult, whilst 

 others, again, show that they have not yet attained their fully- 

 developed condition. In this species the eyes are developed, in 

 the adult animal, to a monstrous size, encroaching upon, filling, 

 and enlarging the entire cephalon, and changing its form from that 

 of a narrow fiat projection to one that is laterally broadly ovate 

 and frontally circularly developed — a change of form that ap- 

 pears to have been produced in order to permit the visual organs 

 to attain their greatest increase of dimension. Both pairs of 

 antennae exhibit a more developed condition in the adult than in 

 the young; and in this they differ from Vibilia, where the pos- 

 terior pair only are in an embryonic condition, and bear a close 

 resemblance to those of the young of this genus. 



