Page:Popular Science Monthly Volume 10.djvu/37

From Wikisource
Jump to: navigation, search
This page has been validated.
27
NATURE OF THE INVERTEBRATE BRAIN.

single meeting of such a committee before the Association separates would settle a basis of action and compress itself into a working sub-committee. The time for papers and discussions is past; they have done their work. What the schools and the head-masters want is authoritative guidance—the guidance not only of a blue-book, but of a living leadership, central, commanding, and accessible, to which they may look with confidence, and bow without loss of prestige.

The precision of its dicta will clear up public confusion; its ability, conscientiousness, and popularity, will overawe the clergy; schools and universities will listen respectfully to suggestions echoed by their own best men; and the three great departments of intellectual culture, equal in credit, appliances, and teaching power, will bring out all the faculties and elicit the special aptitudes of every English boy.

"Hinc omne principium, hue refer exitum."[1]

Nature.

 
Rule Segment - Span - 40px.svg Rule Segment - Span - 40px.svg Rule Segment - Flare Left - 12px.svg Rule Segment - Span - 5px.svg Rule Segment - Circle - 6px.svg Rule Segment - Span - 5px.svg Rule Segment - Flare Right - 12px.svg Rule Segment - Span - 40px.svg Rule Segment - Span - 40px.svg

NATURE OF THE INVERTEBRATE BRAIN.
By Professor H. CHARLTON BASTIAN.
II.

IT now remains for us to consider the disposition of the nervous system in some of the principal types of the sub-kingdom Mollusca.

These are animals wholly different in kind from those we have just been considering, mostly aquatic, and all of them devoid of hollow, articulated, locomotor appendages. Their organs of vegetative life attain a disproportionate development. On the other hand, what are termed the "organs of relation" present a wide range of variation, as may be imagined from the fact that while some of the simplest representatives of the Mollusca consist of mere motionless sacs or bags, containing organs of digestion, respiration, circulation, and generation, its more complex forms are active predatory creatures, endowed with remarkable and varied powers of locomotion, and with sense-organs as keen and as highly developed as those of insects. The lower type is represented by the motionless ascidian, and the higher by the active and highly-endowed cuttle-fish.

Omitting any reference to the Polyzoa, we may turn our attention first of all to the Tunicata, of which the solitary ascidians may be taken as the type. They are marine animals, possessing no powers of locomotion, and having no head. The current of sea-water, serving for respiratory purposes, and, at the same time, containing food-particles, enters a large branchial chamber, through an open, funnel-like projection of the investing tunic of the animal, the orifice of which

  1. With this begin, to this refer the end.