NO. 3567 LABIDOCERA JOLLAE GROUP—FLEMINGER 29 
The suggestion that the female feeding current triggers clasping 
by the Pseudodiaptomus male is not without merit; however, cephalic 
appendages appear to beat at relatively low frequencies. Under- 
water, low-frequency signals are probably subject to serious limita- 
tions for directionality and for separation from background noise. 
Such signals could be effective only over relatively short distances. 
Furthermore, no special organs of hearing are known in Crustacea 
(Cohen and Dijkgraaf, 1961). 
Taking note of the commonness of cuticular pores overlying small 
epidermal glands, the abundance of aesthetasks on the Al and the 
more extensive development of the latter in adult males of many 
families, it seems likely that mate recognition, pursuit and receptivity, 
the mating attack and locating of the female genital pore, etc., are 
mediated by chemical trail substances, i.e., pheromones. Feeding 
and swimming currents would serve to disperse these substances. 
Parker (1902), working on Labidocera aestiva, discusses several simple 
experiments which support the idea that the male finds the female 
by means of pheromones. 
Polymorphism in Labidocera diandra 
IMMATURE COPEPODITE STAGES 
Heap-Hooxs.—Head-hooks of the usual form were seen in all 
immature copepodites (fig. 82) from stages II to V. In copepodite 
stage I, found only in collections in and around La Paz Harbor, 
Baja California, in April 1962, both head-hooks and rostrum were 
absent. Except for the absence of head-hooks in adult diandra 
these findings agree with Johnson’s (1935) account of rostrum and 
head-hooks in the ontogeny of L. jollae. 
Regarding the ontogeny of other species of Labidocera, head-hooks 
are lacking in all stages of L. trispinosa, a fact established by Johnson 
(1935) and verified during the present study. For comparative 
purposes, I have also examined immature copepodite stages of other 
species of Labidocera at my disposal (table 6). No instance was 
found that paralleled the secondary loss of head-hooks* seen in 
3 J have found two specimens of Labidocera in collections from Mombasa, 
Kenya (Lusiad Expedition, lat. 4°04’ S, long. 39°39’ E, VII-24-1962, tow 1h 
1824-1829 hrs., tow 2, 1852-1859 hrs., % m net, 3-0 m depth) that agree in all 
particulars with L. kroyeri except that head-hooks are lacking. No younger 
copepodites, males or normal kroyeri females were present in the two samples. 
I have seen normal kroyeri in a collection from Ceylon (Lusiad Expedition, 
VIII-28-1962, 1807-1817 hrs., 1 m net, 3-0 m depth, in Colombo, Ceylon Harbor). 
Brady (1915) included kroyeri in a list of copepods from Durban Bay, South 
Africa, but failed to include notes on its appearance. 
