Chap. YIII. DEVELOPMENT OF AMPHIPODA. 75 



mals 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.^^ It will remind us of the union of the 

 young Isopoda with the larval membrane and of the un- 

 paired " adherent organ " on the nape of the Cladocera, 

 which is remarkably developed in Evadne and persists 

 throughout life ; but in Dai^hnia jpulex, according to 

 Leydig, although present in the young animals, disap- 

 pears v/ithout leaving a trace in the adults. 



The young animal, whilst still in the egg, acquires the 

 full number of its segments and limbs. In cases where 

 segments are amalgamated together, such as the last two 

 segments of the thorax in DuUchia, the last abdominal 

 segments and the tail in Gammarus ambulans and Coro- 



^° In the genera Orchestoldea, Orchestia, Allor ehestes, Montacjua, 

 Batea n. g., Ainphilochus, Atijlus, Microdeutopus, Leucothoe, Melita, 

 Gammarus (according to Meissner and La Valette), Ampliitlioe, Cerapus, 

 Cyrtophium, Corophium, DuUchia, Frotella and Caprella. 



^^ Little as a name may actually atfect the facts, we ouglit 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 state- 

 ments ; 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 pre- 

 sent, 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 until after impregnation, as might 

 be supposed with reference to Ligia, Cassidina and Philoscia. 



