. . dification. It may be a custom amongthe Apodidae to collect eggs under the looseningcuticle ; this certainly seems to be the case fromthe specimen of L. Spitzbergensis above did not bear any appearance of being six large eggs were packed in so tightly thatthey had to be picked out singly with a needle. It is, however, to be expected that the habit of/latc/iiugeggs under the shield would naturally lead tosome special arrangement for times of ecdysis. Hencethe ephippium of the Cladocera, in which a diffe
. . dification. It may be a custom amongthe Apodidae to collect eggs under the looseningcuticle ; this certainly seems to be the case fromthe specimen of L. Spitzbergensis above did not bear any appearance of being six large eggs were packed in so tightly thatthey had to be picked out singly with a needle. It is, however, to be expected that the habit of/latc/iiugeggs under the shield would naturally lead tosome special arrangement for times of ecdysis. Hencethe ephippium of the Cladocera, in which a differen-tiated part of the cuticle containing two eggs is occa-sionally cast off as a modified form of ecdysis. SECT, xv CLASSIFICATION OF CRUSTACEA 271 THE This is the only other group of the Phyllopodaabout which we have a few words to say. The forma-tion of the bivalve shell of these animals has alreadybeen noticed. The question is, How can a perfectbivalve shell, enclosing the whole body, head and all,be deduced from the folding down of the lateral. FIG. 61.—Limnetis brachyurus, 9 O. F. Mtiller (from Bronns Kiasscn itndOrdnungai), to show the position of the head as transition stage between theCladocera and the Estheridas (Fig. 62). halves of a dorsal shield ? It fortunately happensthat we have a series of forms which make the pointquite clear. In the Cladocera, \ve have the shell folded downagainst the sides of the animal, leaving the head quitedistinctly marked off (Fig. 60). In Limnetis we findthe lateral folds of the shell extending more ante-riorly so as partially to enclose the head, the change 272 THE PART II being chiefly due to the bending down of the head inorder to bring it within the shells (Fig. 61). Limnadia and Estheria show the process com-pleted, the head bent down to such an extent asto be entirely enclosed between the bivalve shells j (Fig. 62). The position of the head in these animals,bent ventrally downwards, is in striking contrast toth
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