270 THE APODIM: PARTII 



proportion to the length of the body, into whose shells 

 the eggs would be likely to fall as they swam on their 

 backs ; the older the Apodidae are, the longer the 

 body grows in proportion to the shell, and an egg 

 dropping out of the adult brood pouch would be 

 hardly likely to lodge under the shell, but would fall 

 straight to the bottom of the water, (2) that the 

 arrangement is not calculated for the development of 

 many eggs at a time, such as one finds in the brood 

 pouches and ovaries of adults ; it could only be 

 advantageously used by the young animals at the 

 first commencement of their reproductive activity, 

 when comparatively few eggs issue from the genital 

 apertures. In this way perhaps we may explain the 

 small size of the Cladocera, and also the relatively 

 enormous size of the shield. 



The second case in which the skin is shed with the 

 unhatched eggs in it does not appear to require any 

 special modification. It may be a custom among 

 the Apodidae to collect eggs under the loosening 

 cuticle ; this certainly seems to be the case from 

 the specimen of L. Spitzbergensis above mentioned. 

 It did not bear any appearance of being accident. 

 About six large eggs were packed in so tightly that 

 they had to be picked out singly with a needle. 



It is, however, to be expected that the habit of 

 hatching vggs under the shield would naturally lead to 

 some special arrangement for times of ecdysis. Hence 

 the 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. 



