DEVELOPMENT OF CYCLOPS SIGNATUS CORONATUS. 195 



merous individuals in both stages were found to be present. 

 Later, one cyclops with eleven antennal segments was found with 

 numerous large ova in the ovaries. 



The rearing of the young from the adults proves conclusively 

 that the forms in question are transitional stages in the life his- 

 tory of a form with seventeen segments in the antennae. The 

 experiments show also that C. signatus may become sexually 

 mature in the larval state. 



That this sexually mature young was a true larva, and not a 

 form in which the growth of only the antennae had been retarded, 

 is indicated by the relatively small size of the individual when 

 compared with the adults, by the incomplete number of segments 

 seen in the antennae, and by the transparency of the skin and the 

 general absence of hairs and spines. 



In the formation of the antennal segments there is a constant 

 sequence. The nine-jointed antenna becomes transformed into the 

 ten-jointed antenna by the division of the third segment from the 

 base into two small ones, and the eleven-jointed condition arises 

 from the ten-jointed, by the formation of a short second segment, 

 the permanent second segment of the seventeen-jointed antenna. 

 Occasionally the antennae contain twelve segments, but inter- 

 mediate conditions between the eleven and the seventeen-jointed 

 stages are not frequent. In Signatus, prior to the completion of 

 segmentation in the antennae, two greatly elongated segments 

 (the seventh and eighth in the eleven -jointed stage) break up 

 simultaneously into the required number of small segments, four 

 and three respectively, while the third segment breaks into two, 

 thus providing seventeen segments, the number in the adult. 



In a former paper, " Heterogeny and Variation in Some of 

 the. Copepoda of Long Island," I was of opinion that " some 

 facts point to the probability that the Cold Spring Harbor 

 forms . . . are morphologically undeveloped." I am now con- 

 vinced that those cyclops combining nine, ten and eleven joints 

 in the antennae, with a two -jointed fifth foot, having a distal seg- 

 ment armed with three undeveloped hairs, are transitional stages 

 in the life history of C. signatus, although the variety is less 

 easily determined. 



The study of various larval stages of C. signatus shows the rudi- 



