SECT. XV CLASSIFICATION OF CRUSTACEA 



269 



the shell in which it is to develop. All the altera- 

 tions which we have here described are exactly what 

 we find in the related Cladocera, for instance in the 

 well-known Daphnia pulex or water flea (see Fig. 

 60). 



Fig. 60. — Daphnia (after Glaus), showing tlie brood cavity {be) between the back of 

 the animal and the dorsal fold ; also the position of the head, projecting freely 

 from the folded valves of the shell fold. Cf. Figs. 61 and 62. 



Again, as to the great difference in size between 

 the Cladocera and the Apodidae, it is perhaps worth 

 .suggesting (i) that it would originally be only very 

 young Apodidse, whose shells were specially .large in 



