NOTES. 
387 
79 The first trace of muscular tissue is found in the stem of Vorticella—an 
Infusorian. In Hydra we find neuro-muscular cells, and the Jelly-fishes 
have muscular tissue. 
80 The muscles of some Invertebrates, as Spiders, are yellow. 
The muscles of the heart and gullet are striped. In the lower animals 
these distinctions of voluntary and involuntary, striated and smooth, solid 
and hollow, muscles can seldom be made. 
The skeleton of the Carrion-crow, for example, weighs, when dry, only 
twenty-three grains. 
The Dragon-fly can outstrip the Swallow; nay, it can do in the air more 
than any bird—it can fly backward and sidelong, to right or left, as well as 
forward, and alter its course on the instant without turning. It makes twen- 
ty-eight beats per second with its wings; while the Bee makes one hundred 
and ninety, and the House-fly three hundred and thirty. The swiftest Kace- 
horse can double the rate of the Salmon. So that Insect, Bird, Quadruped, 
and Fish would be the order according to velocity of movement. 
The theory that Flies adhere by atmospheric pressure is now abandoned. 
85 More precisely, the term brain, or brains, applies only to the cerebrum, 
while the total contents of the cranium are called encephalon. 
86 The exact functions of the cerebrum are not yet clearly understood. 
If we remove it from Fishes, or even Birds, their voluntary movements are 
little atfected; while the Amphioxus, the lowest of Fishes, has no brain at 
all, but its life is regulated by the spinal cord. Such mutilated animals, 
however, make no intelligent efforts. The substance of the cerebrum, as 
also the cerebellum, is insensible, and may be cut away without pain to the 
animal; and when both are thus removed, the animal still retains sensation, 
but not consciousness. 
87 It is very difficult to define sensation, or sensibility. The power is pos¬ 
sessed by animals which have neither nervous system nor consciousness. 
These low manifestations of sensibility are called irritability—the power by 
which an animal is capable of definitely responding to a stimulus from with¬ 
out. The response is not called out by the direct action of the stimulus, but 
is determined mainly by the internal structure and condition of the animal. 
88 Parts destitute of blood-vessels,'as hair, teeth, nails, cartilage, etc., are 
not sensitive. The impressibility of the nerves is proportioned to the activ¬ 
ity of circulation. According to the recent investigations of Dr. Bowditch, 
the channels of motor and sensitive impressions lie in the lateral, and not in 
the anterior and posterior, columns of the spinal cord. 
89 “Tentacles” and “horns” are more or less retractile, while antennae 
are not, but all are hollow. Antennae alone are jointed. 
90 In Man, the soft palate and tonsils also have the power of tasting. 
91 No organ of hearing has been discovered with certainty in the Radiates 
and Spiders. The “ear” of many lower animals is probably an organ for 
perceiving the animal’s position rather than sound—an “equilibrium organ.” 
92 It is wanting in the aquatic Mammals. Crocodiles have the first repre¬ 
sentative of an outsidfe ear in the form of two folds of skin. 
93 This, like the definition of smell and hearing, is loose language. There 
is no such thing as sound till the vibrations strike the tympanum, qor even 
