FLEMINGER: INTEGUMENTAL ORGANS IN GENUS EUCALANUS 



integument and appear as light spots that may 

 be mistaken for perforations. Direct compari- 

 son with a true perforation is helpful to note 

 the reduced intensity of illumination passing 

 through the light spot. Light spots tend to occur 

 in the vicinity of usual perforation sites found in 

 the genus and may represent incomplete or 

 arrested development of a gland or sensillum. 

 Light sj^ots were not recorded as perforations. 



A number of perforations relatively difficult 

 to observe were not examined systematically. 

 They include the dorsal surface of the furcal 

 rami and cephalolateral sites in the vicinity of 

 the first and second maxillae and the maxilliped. 

 The ventral surfaces of the prosome appear to 

 have few perforations but were not examined 

 systematically. 



DISTRIBUTION OF 

 INTEGUMENTAL ORGANS 



In each species the three types of sensilla 

 and pores of integumental glands maintain 

 essentially constant topographic relationships 

 in arrangement and number on both the dorsal 

 and lateral surfaces of the body, as seen for in- 

 stance in subtenuis (Figure 3). One notable 

 pattern appearing in all of the species for exam- 

 ple is the distribution of dorsal hair sensilla, 

 two appearing on the second thoracic segment, 

 four on the third, and four on the fourth, the 

 hairs always being arranged in transverse 

 symmetrical rows, two hairs in each row (Fig- 

 ure 3). Another type of persistent pattern is 

 the regular occurrence of the peg sensillum 

 adjacent to the pore of an integumental gland 

 (Figure 2). The organs are distributed in bi- 

 laterally symmetrical patterns that exhibit 

 serial homologies. Serial homology is indicated 

 by the partial to complete repetition of patterns 

 in adjacent segments. As is shown below in 

 the account of the different species, the closer 

 the general morphological similarities between 

 individual pairs of species the more similar the 

 overall perforation patterns. 



Every morphological type of sensillum or 

 gland pore occupies a topographically unique 

 position, i.e., a designated site within the frame- 



I 



work of the overall bilaterally symmetrical 

 pattern. The designated sites appear in KOH- 

 treated specimens as morpholigically distinctive 

 perforations in the integument. Each body seg- 

 ment has a constant number of organs (Table 3) 

 arranged in a distinctive pattern that is repeat- 

 ed with negligible variation within the series of 

 specimens representing the species. Hence on 

 an empirical basis the appearance of the same 

 type of perforation in approximately the same 

 topographic relationship in the series of spec- 

 imens representing the species is compelling 

 evidence that similarly positioned organs of the 

 same type are homologous among individuals 

 of the same species. That is, they appear to bear 

 the morphogenetic relationships that are a 

 primary basis for regarding the same cephalic 

 or thoracic appendage among individuals of a 

 population as being homologous. Thus the ar- 

 ray of regularly a])pearing integumental organs 

 (designated sites) among the individuals of the 

 species is assumed to comprise a homologous 

 set characteristic of the species. 



Among the species of a species group, integu- 

 mental organs appearing in topographically 

 similar positions on the same body segment in 

 all of the species are viewed as comprising a 

 homologous set characteristic of the species 

 group. The integumental organs common to 

 the various species groups comprise the homo- 

 logous set characterizing the genus. The imi)lica- 

 tion of phylogenetic redundancies is seen in 

 comparing perforation patterns among the 

 species (see Figures 9, IL 13, 15) presented 

 below and in a segment-by-segment comparison 

 of the number of regularly appearing sites in 

 the species and species groups (see Table 3 and 

 Figures 8, 9, 11, 13, 15). 



In the case of a fused series of somites, i.e., 

 a tagma such as the cephalosome, the patterns 

 are arranged in accord with the sets of body 

 appendages in the tagma. The number of ho- 

 mologous sites within the members of a species 

 group is relatively high (cf. Figure 8 with 

 Figures 9, 11, 13, 15) and the number of homol- 

 ogous sites within the genus (55) is remarkably 

 high (Figure 6) considering that the species 

 range from a low of 83 sites in loiigiceps to a 

 high of 131 shared by bimgii and califonticus 

 (Table 3). 



977 



