INVESTIGATION INTO THE CLASP REFLEX OF XENOHIS LAEVIS

Abstract

Recently ethologists have drawn attention to "form-constant"

or stereotyped, behaviour which may be tired off by specific

environmental releasers or displayed "in vacuo" without stimulation.

An important feature of form-constant behaviour is that it is

exhibited by animals reared in complete isolation. Q3n.s has led

to the conclusion that animals "have got" certain innate behaviour

patterns just as they have got inherited morphological features.

These innate patterns are characteristic of the species to which

the animal belongs.

The rigidity of form-constant behaviour must be reflected to

some extent in the activity of the centres and circuits which

comprise the central nervous system (CIS). Some patterned

physiological system must exist in the Cl:S which is responsible for

the coordination of these stereotyped yet species specific patterns.

It can be postulated that animals which display a high degree of

form-constant behaviour possess an elementary and rigid CNS. This

appears to be so; the degree of rigidity of behaviour appears to

depend upon the degree of difierentiation of the forebrain; that is, the

development of the cortex and association areas. Beach (1942) points out

that in mammals "the highly involved nature of the forebrain manifests

itself in complex and plastic behaviour" in which the form-constant

aspects are virtually obscured. This naturally complicates any

interpretation of the functioning of the mammalian CNS. In spite

of this, nearly all neurological investigation is carried out on

mammals.

The behaviour of lower vertebrates is far less variable;

discrete patterns and their specific stimuli can be distinguished

with comparative ease. This is reflected in the relatively simpler

organisation of the CNS of lower vertebrates in which, as Beach points

out, "each area in the forebrain is dominated by a single functional