274 THEO. T. GROOM. 



of the labrum of the Nauplius, but belong to the mandibles. 

 Judging by analogy the palp will represent the ramus of this 

 appendage, the mandible proper being the gnathobase. 



Of the two pairs of maxillae, the first pair are indicated after 

 the first moult undergone by the Nauplius by a row of bristles 

 which has been termed the extra-maxillary arc (No. 12). At a 

 later stage this becomes a small foliaceous appendage (fig. 13) 

 provided with a number of bristles, and already correctly 

 regarded by Glaus as an early condition of the " outer 

 maxilla" (No. 8). Inside this the first maxilla of the Cypris- 

 stage clearly arises (fig. 13). The second pair of maxillae 

 appear later, simultaneously with the six pairsof cirri; they arise, 

 as described by Glaus, just in front of the first pair of the latter, 

 and are clearly serially homologous with the thoracic appen- 

 dages. Further details as to the origin of the two pairs of 

 maxillse will be given on a future occasion. 



It may be regarded as tolerably certain from what has been 

 said above that : 



(1) The antennae of the Nauplius become definitely lost 

 with the moult resulting in the production of the Gypris- 

 stage. 



(2) The biramous mandibles of the Nauplius become reduced 

 at the same time to the small mandibles, the ramus being 

 probably preserved in the form of the small palp. 



(3) The first pair of maxillae arise behind the mandibles, and 

 at a later date, as a small pair of foliaceous appendages. 



(4) The second pair of maxillae arise still later just in front 

 of the first pair of thoracic legs (cirri). 



The mandibles, first maxillae and second maxillae are accord- 

 ingly developed consecutively in the order named. They 

 cannot be regarded as parts of a single or fourth pair of 

 appendages as MetschuikofF maintains, neither can the two 

 pairs of maxillae be regarded as outer and inner parts of a 

 single pair of appendages as Glaus suggests. The mandibles 

 of the Nauplius are not lost as many authors have maintained, 

 but give rise, as Glaus supposes, to the mandibles of the 

 Cypris-stage. The jaws represent, then, the third, fourth, 



