MOUTH-PARTS OF THE CYPRIS-STAGE OF BALANUS. 269 



On the Mouth-parts of the Cypris-stage of 

 Balanus. 



By 



Theo. T. Orooni, F.Z.S., 



Late Scholar of St. Jolm's College, Cambridge. 



With Plate 29. 



The buccal mass of all ordinary Cirripedes consists, as is 

 well known, of three pairs of jaws, together with the labrum 

 and palps. The form and disposition of these mouth-organs 

 in the various genera of the Thoracica has been well investi- 

 gated by Darwin, and the differences observed between the 

 different forms in respect to these parts have been utilised for 

 purposes of classification. The morphological significance of 

 the jaws has, however, never been satisfactorily ascertained, 

 and the current views are all practically based upon supposi- 

 tions, the actual development having been traced in no case. 



Darwin (Nos. 1 and 2) regarded the frontal filaments seen 

 in the larva as the first pair of appendages, and taking the 

 eyes to mark the first segment of the head, and believing that 

 the prehensile antennules arose within the fronto-lateral horns, 

 and that the three pairs of jaws arose in front of the Nauplius 

 appendages, regarded the mandibles of the adult as the appen- 

 dages of the fourth segment of the typical Crustacean, and the 

 two pairs of maxillse as the fifth and sixth respectively. 



The eyes, however, are now no longer regarded as modified 

 appendages ; the frontal filaments, too, have been more cor- 

 rectly regarded as sense-organs, and the fronto-lateral horns 

 have been proved by Claus and others to be glandular processes 

 of the carapace. 



