HETEROGENY AND VARIATION IN COPEPODA. 157 



that this apparently stable individual with the fourteen-jointed 

 antennae represents but a temporary condition in the develop- 

 ment of a form with seventeen antennal segments. In the case 

 referred to, the long eighth joint, that is characterized by three 

 rather widely separated setae, showed distinct, transverse lines 

 across the segment at the level of each of the two lateral setae. 

 Half way up the remaining section, a slight indentation in the 

 cuticle marked the position of the wall that completes the sepa- 

 ration of this long segment into four small ones of almost equal 

 size. 



The breaking up of the eighth segment in the manner indi- 

 cated by these markings gives to the seventeen -jointed antenna 

 a short eighth segment with a single distal seta ; a short ninth 



o o o 



segment with a distal seta ; a short tenth segment without any 

 armature, and a short eleventh segment with one distal seta. 

 These are precisely the conditions which prevail in the seventeen- 

 jointed antennas. 



In his report on " The Entomostraca of Minnesota," Herrick 

 describes a Cyclops strikingly like the one from Jamaica, Long 

 Island, ivitJi fourteen-jointed antenna, three-jointed raini ivith the 

 armature of the last joints like that given for C. parcus, and u'ith 

 a two-jointed fifth foot " with the armature like C. strenmis , which 

 also resembles C. piilc/icHits." The stylets are very long. These 

 correlated peculiarities of structure are recognized as constitut- 

 ing a distinct species known as Cyclops insignis (Claus). Her- 

 rick mentions that "in a previous edition it was suggested that 

 this is but an atavistic form of C. pnlchelhts - - C. strenmis. " If 

 C. strenmis is to be regarded as practically the same form as C. 

 abyssontm, as Schmeil suggests, the Long Island form can hardly 

 be brought into relation with it, for the armature of the swim- 

 ming feet, which is remarkably constant in forms of equal size, 

 differs markedly in the two cases. Schmeil, however, seems to 

 attach little importance to this fact. 



That the Long Island form with the fourteen-jointed antennae 

 represents a transitional stage in the development of a seventeen- 

 jointed form, there can be little doubt, though the determining 

 of the species in the terms of an old and confused classification 

 is by no means an easy matter. The length of the caudal stylets 



