302
P. 9. XEADOWS AND J. I. CABU'BEI&
(1967) has adopted a similar approach by transplanting adult Entobdella
soleae (Trematoda) onto abnormal host species of fish. In this instance,
however, the abnormal host exhibited no rejection reaction but even
so, the parasites only survived for a short while. Kearn also attempted
to infect an abnormal host with the species, oncomiracidia larvae, which
subsequently grew but did not reach sexual maturity. We consider
these are most important papers, not only in their own right, but also
in their relation to habitat selection and the development of commensal
and parasitic associations in general.
Host finding and habitat selection by commensals and parasites,
therefore, offer a wide range of research opportunities. Apart from the
examples already referred to, little is known of how young or larval
commensals and parasites find their hosts (Hazlett and Provenzano,
1965; Kearn, 1967; Carton, 19680; Paling, 1969). Perhaps the greatest
gap in our knowledge, however, concerns the behavioural mechanisms
by which commensal and parasitic associations are set up and
maintained amongst freshwater invertebrates (Fasten, 1913; Herter,
1928, 1929; Welsh,l930, 1931).
IV. THE BIOLOGICAL ENVIRONMENT
The reactions of animals to their biological environment and the
part these play in habitat selection are very varied, and have been considered from a number of points of view by different authors. We will
consider firstly the behaviour of larvae as they settle, and then discuss
gregarious behaviour, spacing out, and aggressiveness. As well as
recognizing members of their own and related species, many animals
obtain important environmental clues from plants and micro-organisms,
so these are also discussed. Finally, we refer to studies on feeding preferences, homing, and egg-laying which show that these also may at
certain times affect the distribution of animals.
A . Settlement behaviour
The larvae of a diverse range of marine invertebrates behave very
similarly as settlement approaches (Nelson, 1924 ; Visscher, 1928 ;
Wilson, 1928 ; Prytherch, 1934 ; Cole and Knight-Jones, 1939 ; KnightJones, 1961 ; Isham and Tierney, 1963 ; F0yn and Gjlaen, 1964 ; Sildn,
1964; Crisp, 1961; Crisp and Meadows, 1962; Gee and Knight-Jones,
1962). From leading an essentially planktonic life they move towards
the bottom, and begin to alight periodically on different surfaces,
the alightments becoming more frequent as time goes on. At each
alightment they explore the surface, crawling over it and stopping
from time to time, as well as frequently changing direction. The
P. 9. XEADOWS AND J. I. CABU'BEI&
(1967) has adopted a similar approach by transplanting adult Entobdella
soleae (Trematoda) onto abnormal host species of fish. In this instance,
however, the abnormal host exhibited no rejection reaction but even
so, the parasites only survived for a short while. Kearn also attempted
to infect an abnormal host with the species, oncomiracidia larvae, which
subsequently grew but did not reach sexual maturity. We consider
these are most important papers, not only in their own right, but also
in their relation to habitat selection and the development of commensal
and parasitic associations in general.
Host finding and habitat selection by commensals and parasites,
therefore, offer a wide range of research opportunities. Apart from the
examples already referred to, little is known of how young or larval
commensals and parasites find their hosts (Hazlett and Provenzano,
1965; Kearn, 1967; Carton, 19680; Paling, 1969). Perhaps the greatest
gap in our knowledge, however, concerns the behavioural mechanisms
by which commensal and parasitic associations are set up and
maintained amongst freshwater invertebrates (Fasten, 1913; Herter,
1928, 1929; Welsh,l930, 1931).
IV. THE BIOLOGICAL ENVIRONMENT
The reactions of animals to their biological environment and the
part these play in habitat selection are very varied, and have been considered from a number of points of view by different authors. We will
consider firstly the behaviour of larvae as they settle, and then discuss
gregarious behaviour, spacing out, and aggressiveness. As well as
recognizing members of their own and related species, many animals
obtain important environmental clues from plants and micro-organisms,
so these are also discussed. Finally, we refer to studies on feeding preferences, homing, and egg-laying which show that these also may at
certain times affect the distribution of animals.
A . Settlement behaviour
The larvae of a diverse range of marine invertebrates behave very
similarly as settlement approaches (Nelson, 1924 ; Visscher, 1928 ;
Wilson, 1928 ; Prytherch, 1934 ; Cole and Knight-Jones, 1939 ; KnightJones, 1961 ; Isham and Tierney, 1963 ; F0yn and Gjlaen, 1964 ; Sildn,
1964; Crisp, 1961; Crisp and Meadows, 1962; Gee and Knight-Jones,
1962). From leading an essentially planktonic life they move towards
the bottom, and begin to alight periodically on different surfaces,
the alightments becoming more frequent as time goes on. At each
alightment they explore the surface, crawling over it and stopping
from time to time, as well as frequently changing direction. The