NO. 1783. NORTH AMERICAN LERNMOPODIDJE— WILSON. 201 



developing larva. But the creature inside of this larval integument 

 is very different from an ordinary nauplius. 



Body form of nauj^lius. — If some of the larvae be dissected out of 

 their surrounding envelopes at this stage and mounted under a 

 gentle pressure, they present in dorsal view the general features seen 

 in fig. 10. The body is ovate in outline, the larger end being anterior, 

 the two diameters in the proportion of 7 to 11, and the greatest width 

 about one-third the distance from the anterior end. Only the first 

 two pairs of appendages are visible, corresponding to the first and 

 second antennae, and projecting nearly their length beyond the 

 margin of the body. Around these two pairs of appendages the 

 nauplius cuticle forms lobes or pockets, as can be seen in fig. 12. 

 The anterior pair, the first antennas, are one-jointed and uniramose, 

 of the same diameter throughout, and each terminating in two long 

 plumose setae. 



The second antennae are biramose, the exopod five-jointed, with 

 each joint terminating in a long plumose seta, the endopod indis- 

 tinctly two-jointed and terminated by two plumose setas. 



The body itself is transparent throughout and shows no trace of 

 mouth, stomach, or intestine. The anterior portion is made up of 

 fine granular protoplasm, from which is to be derived the material 

 for the formation of the mouth-parts, the beginnings of the nervous 

 system and sense organs, the larval muscles, and the large frontal 

 gland soon to be described. 



Along either side, parallel with the margin and close to the dorsal 

 surface, is a broad ribbon-like band of striated muscle fibers, the first 

 beginning of the muscular system which is to operate the swimming 



legs. 



The extreme posterior part of the body is curled over ventrally 

 beneath the anterior portion. In a ventral view (fig. 11) it may be 

 seen to consist of a broad and spatulate abdomen, already well differ- 

 entiated from the cephalothorax, and made up like the anterior part 

 of the body of fine grained protoplasm, thickly studded with nuclei. 

 The mandibles and upper lip have not yet appeared externally save 

 as a slight transverse ridge with a knob at either end of it, just behind 

 the bases of the second antennae. The posterior part of the body 

 therefore is like the metanauplius, while the anterior portion is just 

 as typically nauplius, and the two stages are combined in one embryo. 



The entire body is uncolored save for three isolated patches of 

 dark-brown pigment. One of these is on the doreal surface in the 

 center of the widest portion of the body. It is triangular in shape, 

 with one of the corners anterior, and is about one- third of the entire 

 width. The other two patches are on the ventral surface, one on 

 either side near the posterior end of the cephalothorax, and are much 

 smaller than the dorsal one and of no definite shape. 



