On some (South-African Phyllopoda. ] 3 



be detected. Nor is the carapace as yet clearly distinguished, 

 though a slight folding of the skin on each side of the dorsal 

 face undoubtedly indicates the incipient formation of its 

 lateral parts, as in each of these folds the shell-gland is 

 distinctly traced (see fig. 9). The motions of the larva 

 are at first rather imperfect and clumsy, being effected by 

 irregular strokes of the natatory antennæ. It is only after 

 the 1st exuviation has taken place, and the setæ of the 

 antennæ have thereby acquired their plumose garniture, 

 that the rhythmical movements characteristic of the later 

 larval stages, are observed. The development of the larva 

 goes on very rapidly, and after only 24 hours it has assumed 

 the appearance represented in fig. 11, which is drawn from 

 the very same individual, after the lapse of the above- 

 named time. It may now be easily recognized as the off- 

 spring of an Apus, the carapace being already distinctly 

 developed, and the legs in process of formation. The 

 successive changes are easily understood. They consist in 

 the gradual lengthening of the body, the development of 

 additional legs, and the prolongation of the terminal stylets 

 to the caudal filaments. The natatory antennæ still retain 

 their character as the chief locomotory organs; but when 

 the anterior pairs of legs have become more fully developed, 

 a gradual reduction of these limbs, as also of the mandibular 

 legs, may be observed to take place, and at last not even 

 the slightest rudiment of these 2 pairs of limbs, so power- 

 fully developed in the early stages of the larva remains. 

 The animal has now entered the post-larval period of 

 development, during which no other changes are observed 

 than the general growth of the body and the development 

 of additional legs behind the others. 



