4:4 REPORT — 1877. 



In Anceus the functional property is evidently lost, for the male animal 

 ceases in the adult stage to live on substances that require mastication. In 

 this stage it is doubtful if the animal imbibes nourishment even in the form 

 of fluids ; yet the organ retains the general form of a mandible, but is 

 planted, both in position and arrangement, as if it were an antenna. 



In the female, Anceus (Praniza) retains the general form of structure of 

 the young animal, 'when it lived a parasite on fish ; the mandibles are therefore 

 delicate and slender needle-like styles, arranged with the succeeding ap- 

 pendages so as to act together in consort with power as a proboscis or organ 

 of penetration. 



In the genus Cyamus the mandibles appear to be reduced to a ininirnuni, 

 both in physical and functional qualification, and so also in several genera of 

 the Hyperidce. 



The appendages of the fifth pair, the deutognathe of Milne-Edwards's latest 

 nomenclature, are those that are called mdchoires by Milne-Edwards in his 

 ' Hist. Nat. des Crust.,' foot-jaws by many authors, maxiUce in my " Eeport 

 on the British Edriophthalma," and for which Professor Westwood has 

 suggested " sjagnopoda," as the Greek equivalent for this and the succeeding 

 pair of appendages which belong to the mouth. Neither this nor the sixth 

 pair, the tvitognaihe of Milne-Edwards, appears to undergo any change of 

 form with a relative change of function that can be accepted within the 

 meaning of the term correlation. They vary little in character from the larva 

 to the adult Brachyura, and from the Edriophthalma to the Podophthalma. 

 Their functional power is invariably connected with manducation, in which 

 they assist in conveying food to the mouth ; and from the delicacy of their 

 structure compared with other appendages, it is probable that they may have 

 gustatory capabilities ; but of this as yet we have but small independent or 

 structural evidence. 



The seventh pair of appendages is the last that belongs to the cephalon or 

 head. They arc generally absent in the larva of the Brachyurous forms that 

 pass through the zoea stage, and only appear when the animal is approxi- 

 mating the adult condition. From the time that these appendages iii>t 

 appear to that of the permanent form of the adult animal there is little 

 variation in form, but between their external shape in the various orders 

 of Crustacea there is a considerable degree of variation. 



In the Decapoda tho tetartognathe of Milne-Edwards takes an interme- 

 diate character between the maxiUce and gnathopoda, and its functional pro- 

 perties probably assume the character of the former rather than the latter. 



In the Edriophthalma and some Schizopoda they are modified on the type 

 of gnathopoda in the Macrura, and they fulfil the functions of the posterior pair 

 as they exist in the Decapoda ; that is, they act as an operculum, and 

 efficiently protect the mouth and its more delicate appendages. 



The eighth pair of appendages undergoes a very considerable amount of 

 correlation in Crustacean life. In the higher forms they are functionally 

 employed as aiding in mastication. Passing through the Macrura they assimi- 

 late a pediform character of an imperfect type, while in Squilla and tho 

 Amphipods they are developed into a well-formed grasping-organ. Among the 

 Isopoda they are formed as true walking appendages, and differ little from the 

 succeeding pairs except in being somewhat more robust. Among the Phyl- 

 lopoda they assimilate to the larval character, and possibly disappear in some 

 of the lower types. 



The correlation is equally great in the ninth pair of appendages, which, as 

 a general rule, is formed on the same type as the preceding pair. There arc 



