448 ON THE STRUCTURE AND AFFINITIES OF HIMANTOPTERUS 



In their earliest condition these larva possess sessile eyes, a short 

 carapace, a long jointed abdomen without appendages, and with the 

 terminal segment sometimes entire, sometimes bifid ; the only ap- 

 pendages beside the minute trophi, consisting of a single pair of 

 antennae and a varying number of maxillipedes, so modified in form, 

 as to serve, in conjunction with the abdomen, as a powerful swimming 

 apparatus. 



The nearest approach to Himantopterus which could be con- 

 structed out of the elements afforded by existing Crustacea, then, 

 would be produced by superinducing upon the general form of a 

 Cumoid Crustacean such a modification of the appendages as we find 

 among the Zoasa;form Macruran larva;. 



It must not be supposed, however, that, because on this account 

 Himantopterus may with some propriety be termed a '■'■larval" 

 form it is therefore an " evibryonic" form, or represents any embryonic 

 stage of Crustacean development. On the contrary, so far as it is 

 ^' la7-val" so far it is not "embryonic" inasmuch as the form of the 

 Decapod larva is a wide and sudden deviation from the regular course 

 of embryonic development in the Crustaceans in apparent adaptation 

 to peculiar exigencies. 



Nothing has produced more confusion in the application of natural 

 history to geological problems than the ambiguous use of the word 

 " embryonic," applied as it is, sometimes in^ the sense of " correspond- 

 ence with a developmental stage," sometimes in that of "similarity 

 to a larval condition." The structure of Himantopterus is anything 

 but embryonic in the former, proper sense, — very much so in the 

 latter. 



