10 



THE CRUSTACEA 



against the appendicular theory, and the evidence of embryology 

 does not support it. In the development of the Branchiopod 

 Branchipus, Glaus has shown that the eyes are, at their first appear- 

 ance, sessile, and only become pedunculated at a later stage, the 

 lateral lobes of the head on which they are set becoming produced 

 and separated from the rest of the head by a movable articulation 

 (Fig. 5). 



The most important evidence in favour of the appendicular 

 nature of the eye-stalks is that afforded by the phenomena of 



FIG. a. 



Development of ocular peduncles in Branchipns. (After Glaus.) A, head of young larva ; 

 B, head of older larva. I (in A), lateral lobe of the head bearing E, the compound eye. In B 

 this lobe has elongated to form the ocular peduncle, not yet niovably articulated, although one 

 of the muscles for moving it is developed (m). e, unpaired or nauplius eye ; /, frontal sense- 

 organs. 



regeneration. If the eye-stalk be removed from a living prawn or 

 lobster, it is found that, under certain conditions, a many-jointed 

 appendage, like the flagellum of an antennule, may grow in its 

 place. The bearing of such cases of " heteromorphic regeneration " 

 on questions of homology is, however, by no means clear, and their 

 discussion would involve a reconsideration of some of the most 

 fundamental conceptions of current morphology. For the present 

 it must suffice to point out that the appendicular nature of the 

 ocular peduncles cannot be assumed as definitely proved. 



The antennulcs (or first antennae) are almost universally regarded 



