INTRODUCTION. XV 



In some parasitic families these organs undergo an 

 extreme amount of modification. This is much more 

 exaggerated in the Isopoda than in the Amphipoda. 

 Among the Cyami, the oral appendages are all reduced 

 and somewhat modified, but in the Cymothoida, Bopyridce, 

 and Anceida, among the Isopoda, they appear to lose 

 much of their normal character, and fulfil the office of a 

 sucking apparatus. In the formation of this organ one 

 or more pairs of the appendages may be implicated, as 

 is shown in an elaborate memoir by Schiodte* on the 

 subject. The manner in which the organ is developed in 

 lone from the mandibles, we have described at page 253, 

 vol. ii. of this Work. 



In the Anceida, the appendages of the mouth in the 

 young stage are sharp and lanceolate, the sucking organ 

 being apparently modified from the labrum, where, as 

 in the adult animals, the oral aperture, with the sup- 

 plying appendages, are lost, or converted into members 

 useful for other purposes. 



In the genus Brachyscelus, and others of the family 

 Platyscelida, the appendages of the oral apparatus are 

 reduced to a single pair of membranous leaf-like organs; 

 nor have we been enabled to trace any different character 

 of organ to take the place of the lost ones. Both in the 

 adult and young animal, the mouth appears to be reduced 

 to a rudimentary and simple character : an aperture with 

 the probable power of opening and closing at will being 

 the most that we have been enabled to determine. 



The first or anterior maxillae (Siagnopoda) are separated 

 from the mandibles by a posterior lip, which differs in the 

 Amphipoda or at least in some genera in being cleft lon- 

 gitudinally in the median line, and is termed the labium ; 



* Natur. Hist. Tidssk. 1866, p. 168206. 



