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



can affirm with regard to an Atylus of these [Braailian] seas, remarkable for its plumose 

 branchiae." 



He regards the telson as a segment, notwithstanding its want of appendages. In favour of this 

 view he says, " we have the relation of the intestine, wliich usually opens in this piece, and 

 sometimes even traverses its whole length, as in Microdeutopiift and some other Amphipoda. 

 In Microdeutopus, as Spence Bate has abeady pointed out, one is even led to regard small 

 processes of this tubular caudal piece as rudimentary members." He speaks of the append- 

 ages of the first three pleon-segments as being " reproduced in wearisome uniformity through- 

 out the entire order " of Amphipoda. This remark is not very applicable to Cerapus (see 

 S. I. Smith, 1880), and has a disadvantageous tendency to discourage the examination of 

 these organs in other genera. 



In " Orchestia Daninnii" n. s., he figures two forms of the powerful chelse of the second pair of 

 feet in the male, " two forms united by no intermediate terms." Faxon, on Dimorphism in 

 the Genus Cambarus, 1884, thinks that possibly "these are to be explained iu the same v^ay 

 as the two forms of the male Cambarus, which apjjear to be " alternating periods in the 

 life of the individual," the one form assumed during the pairing seasons, the other in the 

 intervals. 



In Melita Messalina, n. s., and Meh'fa insatiabilis, n. s., in the case of the females " the coxal 

 lamellae of the penultimate pair of feet are produced into hook-like processes, of which the 

 male lays hold with the hands of the first pair of feet." 



He remarks that generally throughout the Amphipoda the heart " extends in the form of a long 

 tube through the six segments following the head, and has three pairs of fissures, furnished 

 with valves, for the entrance of the blood, situated in the second, third, and fourth of these 

 segments," as found by La Valette in Niphargits and by Claus in Phronima. Only in 

 Brachyscelus he found the first pair of fissures wanting to the shortened heart. 



" The Amphipoda," he says, " are distinguishable from the Isopoda at an early period in 

 the egg by the different position of the embryo, the hinder extremity of which is bent 

 downwards. In all the animals of this order which have been examined for it, a 

 peculiar structure makes its appearance very early on the anterior part of the back, by which 

 the embryo is attached to the ' inner egg-membrane,' and which has been called the 

 ' micropylar apparatus,' but improperly as it seems to me." To this statement he appends 

 a note, " Little as a name may actually affect the facts, we ought certainly to confine the 

 name ' micropyle ' to canals of the egg-membrane, which serve for the entrance of the semen. 

 But the outer egg-membrane passes over the ' micropylar apparatus ' of the Amphipoda 

 without any perforation, according to Meissner's and La Valette's own statements ; it appears 

 never to be present before fecundation, attains its greatest development at a subsequent 

 period of the ovular life, and the delicate canals which penetrate it do not even seem to be 

 always present, indeed it seems to belong to the embryo rather than to the egg-membrane. 

 I have never been able to convince myself that the so-called ' inner egg-membrane ' is really 

 of this nature, and not perhaps the earliest larva skin, not formed till after impregnation, as 

 might be supposed with reference to Ligia, Cassidina, and Philoscla." 



" The young animal, whilst still in the egg, acquires the full number of the segments and limbs." 

 In the Hyperinas, indeed, " the young and adults often have a remarkably different appear- 

 ance ; but even in these there is no new formation of body segments, and limbs, but only a 

 gradual transformation of these parts." The sexual differences in Uie Amphipoda are also 

 discussed. 



