1 8 BULLETIN OF THE LABORATORIES 
and project laterally. They are covered with a spiny cuticle, like 
the antennules of the nauplius of Chirocephalus^ 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 antenna, 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.. 
