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. 



81 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. 



82 The skeleton of the Carrion-crow, for example, weighs, when dry, only 

 twenty-three grains. 



83 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 Race- 

 horse can double the rate of the Salmon. So that Insect, Bird, Quadruped, 

 and Fish would be the order according to velocity of movement. 



84 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 affected; 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 4 4 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 outside 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, nor even 



