Terrestrial Amphipoda — Hurley 
119 
Fig. 2. Talorchestia bottae. Three successive stages in development of second gnathopod of male. (After 
Chilton, 1921.) 
diet to that of the supralittoral species, this is 
not unexpected. 
The gnathopod structure, however, does 
show certain modifications. Chilton, in an 
unpublished journal, writes of the "peculiar 
transparent portions of the merus, carpus, 
and propod’ ’ of the gnathopods of Orchestia 
sylvicola and asks, "What can be the function 
of these strange looking structures.^ In them, 
the integument appears semitransparent and 
usually more or less striated, and the joint 
bulges out at these places, but no muscles are 
to be seen in the enlargements." 
Since these processes are absent from the 
male gnathopods in some species, it is un- 
likely that they are primarily connected with 
food or feeding habits; rather, reduction in 
size of the large second gnathopods from the 
condition found in marine and supralittoral 
species, and simultaneous development of 
processes in terrestrial species indicate changes 
in sexual habits as a primary cause. The most 
prominent features of the "pellucid lobes" 
are their lack of musculature, their transparen- 
cy (partly due to the absence of muscle tis- 
sue), and their scabrous surface. They are 
situated on the lower margin of the limb 
which would scrape along the ground and be 
most exposed to external stimuli. These fea- 
tures all suggest to me a tactile sensory func- 
tion. McIntyre, in an unpublished work, has 
described the value of the peculiarly twisted 
female second gnathopod, which is well sup- 
plied with these pellucid processes, in comb- 
ing the broodplates. 
In fact, it does seem likely that there has 
been a change in sexual habits. Williamson 
(1951) studied the mating and breeding of 
