XU THE VOYAGE OF H.M.S. CHALLENGER. 



be called to the superiority wliicli Pallas displays in his descriptions of Amphipoda. In 

 the present century Kroyer can have but few rivals for comliined fulness and accuracy of 

 detail. In the whole multitude of contributions to the voluminous literature here con- 

 sidered, it is obvious that some writers have done more harm than good, or that, to speak 

 in the most lenient terms, their productions are of no value whatever ; but while this can be 

 fairly said only in rare cases, the examples are very numerous of fruitful industry and 

 high scientific excellence. Without, however, any attempt to appraise seriatim the 

 raei'its and services of this host of writers, it may be convenient to mention a few works 

 which the student will find, if not indispensable, at least of foremost value, for particular 

 branches of the subject. Thus, for the general structure of an Amphipod, he should 

 certainly consult the Histoire Naturelle des Crustaces d'eau douce de Norvege, by 

 G. 0. Sars, 1867 ; for embryogeny, the Memoire sur la formation du Blastoderme chez 

 les Amphipodes, les Lerneens et les Copepodes, by E. van Beneden and E. Bessels, 

 1869, and Ulianin's Essay, 1881 ; for the circulation of the blood, the papers by 

 Wrzesniowski, 1879, and Delage, 1881 ; for the family of the Cyamidse, the contri- 

 butions of Llitken, 1873 and 1887 ; for the Caprellidee, Mayer's Die Caprelliden, 

 1882, to which an Appendix is to be presently published ; for the Phronimidae, Glaus' 

 Essay, 1879, and for the Platyscelidse, the same writer's work of 1887; and to this 

 list the treatise by Bovallius on the Amphipoda Hyperina, and that by Wrzesniowski 

 on the subterranean Amphipods, when completed, will doubtless need to be added. For 

 the study of the Amphipoda Gammarina the works of importance are so numerous that it 

 might be misleading to point out a few as more prominently essential than the rest, 

 yet on the difiicult subject of the (Ediceridse the paper by J. Sparre Schneider in 1883 

 ought not to be overlooked. 



Classification. — The division of the Amphipoda into three groups, the Gammarina., 

 Caj)rellina, and Hyperina, has been long and widely accepted, and is followed in this 

 Report as of practical utility and based on reasonable grounds. Geology is unfortunately 

 almost silent about these Crustacea. To all intents and purposes there have been as yet 

 no fossil Amphipods discovered.^ If, nevertheless, we may assume the three groups to 

 have been all derived from a common ancestral form, then the evidence of the groups 

 themselves may be taken to show that the Gammarina and Caprellina, by their similar 

 mouth organs, are more nearly connected with one another than either with the 

 Hjrperina, and that the Hyperina, in respect of their mouth organs, are furthest removed 

 from the primitive form, inasmuch as their maxillipeds have lost that resemblance to 

 modified legs which is so striking in the other two groups. From both the Gammarina 

 and the Hyperina the Caprellina are separated by the slight development of the pleon. 

 This character can be readily explained as an acquired adaptation to their habits of life. 

 If the suggestion be made that the ample pleon might as well have been developed from 



1 See [ip. Ill, 118, 276, 300, 353, 409, 471, 486. 



