52 KINGSLEY. [Vol. VI I. 



early day; the fourth forms the structure called by Watase 

 ('89 and '90^) the "dorsal organ," which early reaches a large 

 size and then disappears ; while I believe that the fifth gives 

 rise to the compound eye.^ I now believe that this account 

 will require serious modification. Of the existence of the organs 

 there is no doubt, but their fate is in question. 



Stage G (Fig. 32) is characterized by the relative change in 

 position of mouth and the first pair of limbs. At first the 

 mouth is distinctly pre-appendicular {vide Figs. 27, 28, 29). At 

 this time its shape is approximately circular. Soon, however, 

 the mouth becomes more elongate, its front margin becoming 

 acute as if the right and left lips were coalescing (Figs. 30, 31). 

 By this process a true ectodermal stomodaeum is invaginated, 

 and the mouth is carried backward, as I have already explained 

 and diagrammatically illustrated ('85, PI. XXXIX, p. 526, Figs. 

 40-43), so that as a result the first pair of appendages become 

 distinctly post-oral. Other features are the budding of the 

 curious appendix (flabellum Auct.; appendice lanceole de la 

 hanche, van der Hoeven) upon the basal joint of the sixth pair 

 of appendages ; and the outlining of the so-called metastoma 

 upon the sixth body segment. I have already pointed out that 

 this last cannot be regarded as an appendage of a metameric 

 nature (Self, '85, p. 532), since it is borne on the same segment 

 as the true sixth appendage. 



In Stage H, Fig. 33 (Packard, Fig. 19; Kingsley, '85, Fig. 12), 

 the distinction between cephalothorax and abdomen is evident ; 

 the legs are longer and show evident segmentation. (Fig. 33.) 



In Stage I (Kingsley, '85, Fig. 14; Packard, Fig. 24) the 

 appearance is quite like that of the adult. The body is now 

 much more depressed, the legs are like those of the adult, and 

 the cephalothorax is considerably larger than the abdomen. 

 The abdomen exhibits traces of segmentation, while its margin 

 bears the movable spines upon its margin which are character- 

 istic of the adult. The telson as yet remains as a slight lobe of 

 the middle of the hinder margin of the abdomen. 



^ This account varies from that of Patten, ('90) if I understand him correctly. 

 According to him the median eye falls outside the category of these organs. The 

 compound eye (" convex eye ") " arises from three small sense organs near the third 

 thoracic segment," while the " eye of the fourth segment " is very large, thus putting 

 the compound eye in front of the ' dorsal organ.' Watase, on the other hand ('90^) 

 places the compound eye behind the dorsal organ. (See Postscript.) 



