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PROCEEDINGS OF THE NATIONAL MUSEUM. 



vol. xxvi r i. 



strong sternum, which is thickened along its anterior edge (fig. 44). The 

 sternum uniting the second pair is very short and is made up of two 

 heart-shaped plates inclined toward each other and united at their tips 

 and for some distance along their adjacent sides (fig. 45). 



The endopods and exopods of the two pairs of legs are quite similar 

 and each consists of a single joint, broadly lamellar and fringed dis- 

 tally with six large plumose setae, making them strong swimming 



organs. In the arrangement of these 

 seta? may be seen an indication of the 

 future segmentation of the append- 

 ages. Upon the third free segment 

 may be found a pair of small projec- 

 tions, unsegmented and unbranched, 

 which are the rudiments of the third 

 pair of legs. Each carries at its 

 distal end several short spines. 



Fig. 44.— Fikst swimming legs of metanau- 

 PLIUS OP Caligus bonito. Ventbal view, 



SHOWING CONNECTING VENTRAL PLATE. 



At the third moult, which occurs 

 after about the same interval as 

 the others, there is little advance 

 save in a few changes toward the 

 adult form. The first antennas now 

 become three-jointed, the basal 

 joints long and narrow and turned 

 back on and articulated with the 

 anterior margin of the^ carapace. 



It is plainly evident that they 

 are to become the frontal plates. 



Between them, in the very front of the head, there appears a large 

 median gland which secretes the material for attachment during the 

 following chalimus stage. (See fig. 46.) This gland is heart-shaped, 

 the larger end -being anterior, and is close to the dorsal surface of the 

 carapace. A duct leads from the gland to a point at the very tip of 

 the carapace between the bases of the first antenna?. 



Fig. 45.— Second swimming legs of meta- 

 nauplius of Caligus bonito. Ventral 

 view, showing connecting ventral 



PLATES. 



