THE SUCTORIAL FORM. 255 
stances it is not, in fact, apparent. All animals be- 
longing to this type are shy, and evince little or no 
propensity to become domesticated. They are without 
offensive protection ; but nature, as if to screen them 
from their enemies, has endowed them with great 
caution, uncommon vitality, and in many cases has 
protected them either with a hard skin or a coating of 
bony armour, which entirely envelopes their body, and 
repels all injury. When compared to the pre-eminent 
examples of their respective circles, the suctorial type may 
be viewed as the most imperfect ; that is, the most simple 
in its organisation, and the most dissimilar from all others. 
(315.) Let us now see in what manner this type is 
developed in the more comprehensive divisions of the 
animal world. The polypes and the animalcula (Acrita) 
are the smallest of all living beings. Thousands are in- 
visible to the naked eye; and these, even when viewed 
under the microscope, appear but as grains of sand, 
mere particles of matter, so simple in their structure as 
often to be without limbs, and only recognised as animals 
from being endowed with voluntary motion. In what 
manner they are nourished, — whether by absorbing the 
fluid in which they live, or by sucking the juices of 
other beings still more imperceptible than themselves, 
—is immaterial to our present purpose, as both are 
obvious modifications of the suctorial process. In 
the vertebrated circle, comprehending the most perfect 
of all animals, this type of imperfection is confined 
to a very small number. Of these the siren of Lin- 
neus is probably the type: it is, perhaps, the most 
defenceless of animals ; living, like the worms, in the 
muddy bottoms of ponds, destitute almost of eyes, with- 
out teeth, and whose feet are so inefficient as to appear 
like unserviceable appendages. In the great division of 
annulose animals we have all these types represented by 
the intestinal worms ; whose structure, indeed, is so im- 
perfectly jointed, that in some of the modern systems 
we find them referred to the Acrita or polypes: they are 
nevertheless truly annulose, and give us the most perfect 
