D, J. SCOURFIELD ON THE WINTER EC4G OF A RARE WATER-FLEA. 175 



moulting of the ephippium have I ever been able to see any 

 special modification of valve margins. I am inclined to think, 

 therefore, that the retention of the valve margins in this case is 

 more or less a matter of accident, although it is evidently a step 

 in the direction of the very perfect modification exhibited by 

 Leydigia acanthocercoides. 



As regards the structure of the main portion of the proto- 

 ephippium of L. acanthocercoides the following facts were noticed. 

 The usual chitinous thickening along ithe dorsal edge was very 

 well developed ; not so much comparatively as in Chjdorus 

 sphcericus, but much more than in the majority of the Lynceidse. 

 The outer shell still retained its primitive striation, though the 

 lines seemed more confused, as if they had been thickened by 

 irregular deposits of chitin. The most pecnhar feature about the 

 structure of the proto-ephippium, however, was that the whole of 

 the space between the outer case and the Qgg was filled with a 

 mass of tissue consisting of irregularly polyhedral cells (see Fig. 5). 

 This was so thick that, combined with the abundant deposit of 

 pigment in the outer case, the resting Qgg itself could only be 

 seen in a very ill- defined way. I may remark here that I have 

 noticed the existence of somewhat similar cellular tissue in the 

 proto-ephippium of Alona tenuicaudis. It is, no doubt, an extreme 

 development of the delicate inner membrane which I have found 

 to surround the Qgg in nearly all proto-ephippia, and is homologous 

 to the definitely formed inner capsule of such typical ephippia as 

 those of Baphnia magna and its nearest allies. Its chief function 

 is obviously to form a' soft spongy " packing " around the Q^;g^ and 

 so to more effectually preserve the latter from injury. When the 

 proto-ephippium of L. acanthocercoides w^as viewed from the front 

 (see Fig. 4), the two valves were seen not to quite meet along the 

 middle line, but the space between them was effectually closed by 

 the inner cellular tissue. Towards the posterior end, this " pack- 

 ing" was so plentiful that it protruded from the shell as shown in 

 Fig. 3, and it was here that its structure could be best made out. 

 The limits of the cellular tissue within the outer case were fairly 

 definite, and are shown in the figure just referred to by the line 

 bounding the darker portion of the proto-ephippium. 



From the foregoing description of the proto-ephippium of 

 L. acanthocercoides it will be seen that in no less than three 

 respects it is considerably in advance of that of Chydorus sphcericus, 



