1 8 BULLETIN OF THE LABORATORIES 



and project laterally. They are covered with a spiny cuticle, like 

 the antennules of the nauplius of Cimvcephaliis, but are less movable 

 and less obviously tactile organs. It has been denied that these are 

 really antennae, but the history of their further development makes it 

 clear that they are really representatives of those organs, though ob- 

 scured by their covering. 



Although the nauplius of Limnetes is said by authors (Packard, 

 Monogr. Phyllopod Crust, etc.) to be distinguished from other nauplii 

 by the small size of the labrum, this is founded upon a mistake. The 

 labrum is really the most prominent of the larval organs. It is, 

 indeed, of monstrous form and is so enlarged as to become a valve 

 nearly as large as the shield-like expansion of the body above. The 

 larva resembles a small turtle, from the edge of whose shell protrude 

 two pairs of appendages. 



The labrum is thorned, as is the whole body, and is slightly, if at 

 all, movable. In this respect it differs little from other young nauplii. 

 Like the first pair of antennae, the labrum is obscured by its larval 

 envelope, similar to that which extends the carapace of the body to 

 form a false shell. The second antennae are of the usual form among 

 Phyllopods, the anterior branch being five-, the lower one two-jointed. 

 The basal portion is furnished with a prominence bearing two heavy 

 claws. The palp of the mandible is of the usual form. 



In the next stages slow changes accompany the increase in size- 

 A dorsal area is marked off over the maxillary and mandiblar seg- 

 ments, from which the shell develops under the larval covering. The 

 nauplius eye becomes associated with a pair of club-shaped sensory 

 hairs. A ventral swelling becomes distinct and proceeds to segment 

 itself and elaborate limbs. (Fig. i, Plate VII.) In figure ii of this 

 plate, which gives a semi-diagramatic under view of the abdomen, is 

 shown that, as in other Phyllopods, the appendiculate segments seem 

 to appear at once and the development goes on then from before back- 

 ward. Prior to the appearance of feet (stage of Fig. i.) the animal 

 is about 0.33 mm. long, but becomes over 0.50 mm., before the meta- 

 morphosis. In the last stage prior to assuming the characteristics of 

 the adult, the antennules seem smaller, the labrum has become cordate 

 and very wide, while a prominence appears below the eye. Rudi- 

 ments of the compound eye are visible and the sensory filaments over- 

 lying the pigment fleck are developed. The anterior part of the 

 digestive tract has bifurcated and its branches extend, toward the labrum- 



