208 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



this occasions no break in the continuity. Development goes on 

 inside of it through the naupHus and metanauphus stages just as if 

 it were not present. 



FIRST COPEPODID OR FREE-SWIMMING STAGE. 



BODY FORM. 



As the larva emerges in this stage from the egg it appears in a form 

 which, by the segmentation of the body and by the structure of the 

 appendages, corresponds with the first cyclops stage of free-swimmere 

 (fig. 23). The body is much elongated and flattened dorso-ventrally; 

 the cephalothorax is elliptical, and nearly twice as long as wide, the 

 proportion being as that of 9 to 17. It is enlarged at the anterior 

 corners above the bases of the second antennae, and furnished with a 

 distinct notch on either side and a dorsal groove between the head 

 and first thorax segment. It is slightly arched dorsally, but flat on 

 the ventral surface, and carries at its posterior end a wide obcordate 

 process, which projects over the base of the second thorax segment. 



The shorter and smaller posterior portion of the body is made up 

 of four segments, sharply separated from one another, the last one 

 carrying the broad anal setae. 



The first of these segments, the second thoracic, is the largest and 

 the third one is the smallest. The first one is half the width of the 

 cephalothorax and has a broad, semicircular, posterior process. The 

 remaining segments are all the same width, which is half that of the 

 first segment. 



On each side of the second one at the center is a smah papilla, armed 

 with a single long spine, the rudiments of a third pair of swimming 

 legs. The last segment, which is a fusion of the posterior thoracic and 

 abdominal segments, is subquadrilateral in outline, with nearly 

 straight sides. 



The anal laminae are large and broad, and each carries three 

 long and three short setae. The total length of this larva is 0.48 

 mm. Length of cephalothorax, 0.32 mm. Width of same, 0.165 

 mm. Length of free thorax, 0.12 mm. Width of first free segment, 

 0.08 mm. 



These larvae are transparent and colorless except for four patches 

 of dark brown pigment, one dorsal, the other three ventral. The 

 dorsal patch corresponds to that already described in the nauphus, 

 but has enlarged considerably. 



The posterior ventral patch includes the two ventral ones of 

 the nauplius, which are now darker in color and have enlarged 

 until they are fused across the midline (fig. 22). In addition, there 

 is a small anterior patch on either side just behind the base of the 

 maxilliped. 



