174 D, J. SCOURFIELD ON THE WINTER EGG OF A RARE WATER-FLEA. 



have become converted into two enormous hooks. With a few 

 touches of a small brush I was able, with a second specimen which 

 was secured directly after being thrown off, to remove all the un- 

 modified parts of the carapace, etc., and then the proto-ephippium 

 appeared as shown in Figs. 3 and 4, w^hich give lateral and ventral 

 views respectively of this very peculiar structure. Later in the 

 year, November 5 th, I was fortunate enough to find at Richmond 

 Park another specimen of this proto-ephippium exactly in this 

 condition. 



8o far as I know, this structure exhibits the most highly 

 developed adaptation for dispersal * that has jet been seen among 

 the resting eggs of the Cladocera. As a rule ephippia and proto- 

 ephippia are not provided with hooks, spines, or any such con- 

 trivances for dispersal. The principal exception to this is that 

 the ephippia of Daphnias belonging to the D. mag^ia group are 

 usually furnished wdth anterior and posterior extensions of the 

 dorsal margin which are closely set with little recurved teeth. 

 A good example of this is shown by Sars in the figure of the 

 ephippium of Daphnia lumholtzi in his paper " On some Australian 

 Cladocera raised from dried mud" (6). In D. magna itself, more- 

 over, more or less considerable portions of the free margins of the 

 valves may also remain attached to the ephippium, as was shown 

 by F. A. Smitt in his paper " Sur les Ephippies des Daphnies" 

 (12). In fact, his figure of the ephippium of D. magna (PI. IV. 

 Fig. 1) shows a quite remarkable similarity in this respect to 

 what has just been described in the case of L. acanthocercoides. 

 But the attachment of the shell margins to the ephippium of 

 D. magna, at least to the extent figured by Smitt, does not seem 

 to be usual. So far as I know, Smitt is the only author who has 

 mentioned such an arrangement, although the ephippia of this 

 species have been referred to again and again. I have myself 

 examined a fair number of these ephippia, but only rarely have 

 I seen portions of the shell margins still attached to them, and 

 I have never in any case found more than about half the posterior 

 margin so attached. Further, neither before nor after the 



* I believe that dispersal and not anchoring is the object served by such 

 adaptations, because of the impossibility of conceiving how the anchoring of 

 resting eggs could be of benefit to animals like the Cladocera, which live 

 almost wholly in still waters, while on the other hand the advantages of 

 dispersal are apparent. 



