276 THEO. T. GROOM. 



EXPLANATION OF PLATE 29, 



Illustrating Mr. Theo. T. Groom's paper, " On the Mouth- 

 parts of the Cypris-stage of Balanus." 



Fig. 1. — Side view of buccal mass of Cypris-stage of Balanus balanoides. 

 Mandible. Mandible with {palp) its palp. mx^. and mx^. First and second 

 maxilla}, sliowing chitinous process between their bases, bucc. m. musl. 

 Muscles supplying buccal mass. Thoracic muscles. Muscles filling up the first 

 segment of the thorax. 



Fig. 2. — View of same from in front. Letters as in Fig. 1. Also, adductor. 

 Adductor muscle of carapace. 



Fig. 3. — View of same from behind. 



Fig. 4. — Similar view, the form of the appendages being shown by trans- 

 parency. 



Fig. 5. — Mandible and its palp. 



Fig. 6. — View of first maxilla", from outside. 



Fig. 7. — View of same from side. 



Fig. 8. — View of second maxillae from side. 



Fig. 9. — Side view of an immature Cypris-stage of an undetermined species 

 of Balanus from Jersey, adductor. Adductor muscle of carapace, ant^. 

 Antennule. anl"^. Antenna, caudal app. Caudal appendage, compd. eye. 

 Compound eye. frl. aperture. Aperture of fronto-lateral gland, mx^. First 

 maxillae, mx^. Second maxillae, palp. Palp of mandible. 



Fig. 10. — Ventral view of similar larva. Lettering as in Fig. 9. Also, 

 ant^. muscles. Muscles to antennule. cp. edge. Edge of carapace. 



Fig. 11. — Ventral view of mouth-organs of a larva in a somewhat more 

 advanced stage. The labrum is now greatly reduced, and the sites of the 

 antennae barely recognisable. 



Fig. 12. — View of labrum and bases of antenuules, and antennae with 

 their sockets {ant^. sock., anf. sock.) of the last Nauplius-stage of a species 

 of Balanus from Jersey, mandible sock. Socket of mandible. 



Fig. 13. — View of the developing maxillae {mx^. and m.r'.) of the Cypris- 

 stage, as seen in a similar Nauplius. The small setigerous first maxillae are 

 external, while the two pairs of pupal maxillae are underneath the cuticle ; 

 the first pair of tiiese has the tip slightly withdrawn from the external 

 maxillae, inside which they were formed. 



