316 THE ZOOLOGIST. 
writers, modified in a variety of ways, becomes an important 
factor in all that relates to adaptation to ‘“‘nocturnism,” if such 
an expression is admissible. 
Possibly the above and others of the Protozoa are not strictly 
nocturnal, though some shun direct sunlight. But whether heat- 
rays may have a determining influence is an open question. 
Among the Meduse, or Jelly-fish (C@lenterata), which, though 
met with during the day-time, abound most frequently, in calm, 
clear weather, at the surface towards nightfall, or when complete 
darkness has set in, sensory organs of a most rudimentary kind 
are developed. Nerveless, as ordinarily understood, yet, accord- 
ing to the recent researches of Romanes, Eimer and others, 
defined lines of sensory impressions éxist in the sarcodous jelly 
of their umbrella. In fact, reflex action is apparent, minus true 
nerves. A few minute calcareous particles aggregated together 
or within a sac scattered towards the periphery of the umbrella, 
acoustic vesicles, are forerunners of organs of hearing; and for 
eyes there are pigment spots at the base of the tentacles, the 
latter themselves being feelers. 
Thus the Sea-blubbers are instructive as evineing diffused 
sensation along with localized spots wherein this touch becomes, 
by slight differentiation of tissue, instrumental in the production 
of hearing and sight, of course in an inferior degree. Although 
absolute proof is wanting, it is quite within the range of proba- 
bility that their stomachal cavity appreciates in a faint degree 
approaches to a low kind of taste and even smell. In some 
genera more diurnal in habit, their extreme sensitiveness to light 
is manifest by their immediately closing and descending when 
heavy clouds dim the atmosphere. 
The foregoing well illustrates Mr. Herbert Spencer’s views 
(‘Principles of Psychology’), viz.:—‘‘ For every higher phase 
shows itself as an ability to recognise smaller and smaller 
differences, either of kind or degree, in attributes of surrounding 
bodies; and so render it possible still further to specialize the 
adjustment of inner to outer relations.” 
In nocturnal animals this principle is carried to its fullest 
extent, all adaptations to habit being connected with endowment 
of extra sensitiveness specialized. 
The Annelids, however, afford plentiful examples of preference 
for darkness ; and the common earthworm is both easily observed 
