240 D. J. SCOURFIELD ON EPHIPPIA OF LYNCEID ENTOMOSTRACA. 



which is, of course, normally moulted in the same way as the 

 outer highly chitinised shell. In other cases a certain amount of 

 increase in the substance of the membranes has occurred, and 

 even a rudimentary cellular structure developed {e.g. Alona 

 rectangulci), while in not a few species (e.g. Alonojysis ambigita, 

 Alona tenuicaicdis, Leydigia acanthocercoides, Alonella karua), a 

 very elaborate cellular spongy "packing," more or less completely 

 tilling up the whole space between the outer coat of the ephippium 

 and the egg, has been produced. So far as I am aware, this 

 latter development is peculiar to the Lynceidae, and it seems as 

 highly specialised a feature in its own way as the chitinous inner 

 shell found in the ephippia of Daphnia magna and its nearest 

 relatives. 



(7) The ephippium contains but one resting eg^, except in the 

 single genus Euryc&ixus, where numerous eggs occur. 



The genus Eurycercus is so peculiar, both in regard to structure 

 and the great size to which its representatives attain, that it is 

 scarcely surprising to find a well-marked distinction in one point 

 at least in connection with its ephippia and resting eggs. The 

 only other case in which more than a single resting Qg^ has been 

 recorded is Camptocercus macrurits, which, according to Weismann, 

 (12), sometimes, but not always, has two such eggs. In view of 

 the evidence now available in favour of the universal adherence 

 to the principle of one ephippium, one egg, in the sub-family 

 Lynceina, it is certainly desirable that this species should be re- 

 examined in order to ascertain whether the production of two 

 winter eggs can be considered in the slightest degree normal. 



As regards the interesting question of the probable course of 

 evolution among the ephippia of the Lynceidae, we are unfortu- 

 nately not in a position to say very much with certainty. Never- 

 theless, everything seems to point to the fact that ej^hippia have 

 developed out of the very simple process of depositing the resting 

 egg or eggs in the unmodified moulted shell, the delicate inner 

 lining of which would also, no doubt, gather round the egg, being 

 prevented from leaving the outer case by the egg itself. It will 

 be evident, from what has been said above, that there is not a 

 single case known at present which approaches anywhere near 

 this imaginary primitive condition. Even in Alona tenuicaudis, 

 where the whole shell is used as an ephippium, there is a darkening 



