THE PELAGIC FAUNA AND FLORA. 175 
Near the continental lines the pelagic fauna is reinforced by 
numberless pelagic embryos, representing nearly every type of 
marine animal. The polyps (Fig. 63), acalephs, echinoderms 
(Figs. 64, 64a), mollusks (Figs. 65, 66, 67), and articulates (Figs. 
C8, 69, 70, 71, 72, 73, 74, 75, 76), of our coasts, although living 
upon the bottom and on the shores when adult, yet passa por- 
tion of their earlier life as pelagic forms. The Іатуз and young 
of many of these types swarm during the breeding season, and 
often find their way to a considerable distance from the shore. 
With them are associated the eggs (Fig. 77) and embryos of 
a number of our migratory and shore fishes. The 
study of all this pelagic life is very recent. There 
are many types of which the life history is un- 
known, so that it is often difficult to determine 
whether an animal is merely the young of some hit ае 
well-known littoral form or a true pelagic type. lagic Fish Egg. 
Indeed, many of these free-swimming animals, de- P? 
scribed at first as strictly pelagic, have subsequently proved to 
be only embryonic stages of well-known species. 
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Fig. 78. — Plagusia. 4. 
It is probable that among the larval forms of many pelagic 
animals there is, under certain conditions, a retardation of de- 
velopment similar to that known among batrachians. The 
larval stage continues in Plagusia (Fig. 78) and Phyllosoma 
long after the time when the embryo should have passed into 
Rhombodichthys (Fig. 79) and Palinurus. Leptocephalus is 
