272 THEO. T. GROOM. 



Anteriorly the basal portion of the mandible gives oflP a some- 

 what inwardly-curved palp-like process (figs. 1 — 5, palp.). This 

 has all the appearance of being an integral portion of the 

 mandible^ and is filled by a mass of developing muscle con- 

 tinuous with that of the rest of the appendage, and runnings 

 together with the muscle of the two pairs of maxillae, to the 

 anterior part of the thorax (fig. 1). The anterior margin of 

 the basal portion of the mandible (figs. 1 and 5) is apparently 

 very short, though this is difficult to ascertain definitely, since 

 in teased preparations the buccal mass commonly tears away 

 from the head immediately in front of the palp ; it is, thus, 

 easy to see why Claus regarded the palp as belonging equally 

 to the mandible or labrum. The evidence, too, afforded by the 

 muscle-supply must be taken with caution, as Nussbaum (No. 

 11) describes a muscle supplying the mandible in the adult 

 Conchoderma as having its origin in the palp. Tlie evidence, 

 however, afforded by the immature Cypris-stage to be described 

 immediately appears to clearly show that the palp belongs to 

 the mandible. 



The three pairs of gnathites, according to Claus, are situated 

 beneath a labrum; the labrum, however, as a definite promi- 

 nence, is exceedingly small at this stage in Balanus, and 

 projects as a very minute lobe between the distal ends of the 

 palps. The site of the future labrum is, nevertheless, recog- 

 nisable as a broad area in front of and between the mandibles 

 and their palps. The jaws are directed ventrally, so that this 

 area is to be described as situated anteriorly to, rather than 

 below the jaws. 



Some stages of an undetermined species of Balanus ob- 

 tained from Messrs. Sinel and Hornell in Jersey in the spring 

 of the present year (1894) were specially valuable as throwing 

 light on the question of the fate of the Nauplius appendages, 

 and on the homologies of the jaws of the adult. The antennules 

 of the Nauplius, as already pointed out, have long been known 

 to give rise to the prehensile antennules of the Cypris-stage, 

 and these, according to Darwin, can often be recognised in the 

 adult. The fate of the antennae of the Nauplius has not been 



