THE FAUNA OF 'T'HE SEASHORE. 295 
the Echinoderms through Tornaria is very remarkable. Possibly 
Amphioxus once had a Tornaria stage, and has lost it just as 
one species of Balanoglossus has lost it, as Mr. Bateson has 
lately discovered. 
The littoral zone has given off colonists to the other three 
faunal regions. The entire terrestrial fauna has sprung from 
colonists contributed by the littoral zone. Every terrestrial 
Vertebrate bears in its early stages the gill-slits of its aquatic 
ancestor. All organs of aérial respiration are mere modifica- 
tions of apparatus previously connected with aquatic respiration, 
excepting, perhaps, in the case of T'racheata, trachere being most 
likely modifications of skin-glands, as appears probable from 
their condition in Peripatus. The oldest known air-breathing 
animals are insects and scorpions, which have lately been found 
in Silurian strata. Prof. Ray Lancaster believes the lungs of 
Scorpions to be homogeneous with the gill-plates of Limulus. 
Birds were possibly originally developed in connection with 
the seashore, and were fish-eaters like the tooth-bearing Hes- 
perornis. 
The fauna of the coast has not only given rise to the 
terrestrial and fresh-water fauna; it has from time to time 
given additions to the pelagic fauna in return for having thence 
derived its own starting-points. It has also received some 
of these pelagic forms back again, to assume a fresh littoral 
existence. 
The deep-sea fauna has probably been formed almost entirely 
from the littoral, not in the remotest antiquity, but only after 
food derived from the débris of the littoral and terrestrial faunas 
and floras became abundant. 
It is because all terrestrial and deep-sea animal forms have 
passed through a littoral phase of existence, and that the littoral 
animals retain far better than those of any other faunal region 
the recapitulative larval phases by means of which alone the true 
histories of their origins can be recovered, that marine zoological 
laboratories on the coast have made so many brilliant discoveries 
in Zoology during late years. 
