162 JOURNAL OF ENTOMOLOGY AND ZOOLOGY 
there are still many other places in which some one or another 
of this isopod group dwells. Some are securely fortified within 
the minute chambers of the sponges; some are tube builders 
or excavators; some have sought the crevices of the big dry 
rocks where they neighbor with the shore crabs; and some 
are even fond of the muddy shore of a stagnant lagoon; still 
others inhabit the gill chambers of fish or crabs, living a 
parasitic and degenerate life. Though many of the Isopoda 
are marine there are also many terrestrial and fresh-water 
forms, the former known to most of us by their representative, 
the common sow-bug, or wood-louse, or pill-bug, as it is vari- 
ously called. 
Not less interesting than the numbers and habitat of these 
animals is their diversity in color and form as adapted to their 
environment. Those inhabiting the sandy and rocky places are 
provided with a chitinous crusty structure and are colored a 
dull gray or brown which favors well their characteristic love 
for obscurity. Those which dwell in the pools or on the moss 
are more delicate and are provided with special swimming 
organs. On the green Alge there are elongated isopods, green 
in color and hardly distinguishable from the moss on which 
they oceur, and similarly brown forms on the brown Algw. A 
most interesting instance of these color adaptations which I 
observed in my study at Laguna Beach was that of an isopod 
which dwells on the oral surface of a sea urchin; it was a dark 
reddish-purple in color, so very like that of its host that one 
could searcely distinguish it when at rest. Much might be said 
of the diversity and beauty of color of the marine Isopoda, 
but that is a study in itself. 
It appears that the Isopoda and Amphipoda are somewhat 
closely related, since both can be grouped under the more 
limited division, Arthrostraca. They differ from each other 
as follows: the Isopoda are dorso-ventrally flattened, the 
Amphipoda laterally compressed. There are other differences 
such as modified second and third thoracic appendages and a 
differentiation of abdominal segments into two sets in the 
Amphipoda. A common and popular distinction is the crawl- 
