SECT, in THE APPENDAGES 35 



II. Tlie second pair of Antenna (Fig. 7 B) The 

 second antenna is so much reduced in the Apodidaj 

 that its absence has often been considered characteristic 

 of the family. In no specimen examined by us has it 

 been wanting. Its position has already been described 

 (p. 30) as agreeing exactly with that of the correspond- 

 ing antennal parapodium of the Annelids. It has, like 

 the first antenna, been brought in front of the mouth 

 by the bending of the head. Although it is very much 

 degenerated, it shows three divisions, with the slight 

 rudiment of a branch at the end of the second, which 

 is the only trace of its former relatively greater develop- 

 ment as a branched swimming limb in the Nauplius. 

 We deduce the limb from the antennal parapodium of 

 the second segment of the Annelida (cf. Fig. 7 B with 

 Figs. I, 2). Its great reduction in the Apodidae is no 

 doubt due to its being caught, as it were, in the angle 

 of the bend, and further shut in under the shield. In 

 Limulus, owing to the greater space under the shield, 

 it is freer to develop into a chelate foot (see Fig. 43, 

 p. 1 88). In Branchipus also, in which the shield has 

 disappeared, it undergoes no such reduction. 



The second antenna, like the first, stands on a small 

 bulb which may perhaps be homologous with that 

 of the first antenna, but certainly in this case cannot 

 represent the remains of the parapodium. According 

 to our homologies for this limb (see Fig. 7 V) the 

 dorsal parapodium is still present, and forms its 

 proximal half, ending in the minute rudimentary 

 branch shown in the figure. In sections of the basal 

 bulb we found a deep indentation, which led us to 



D 2 



