We can confirm the fact of this sort of fibre being present, but we fancy a reader not versed in the mysteries of physiology exclaiming, 'What does it matter whether his fibres are striped or not?'
Physiologists used to suppose there was a strong and marked distinction and separation between striped muscles, that is, muscles the fibres of which exhibit transverse stripes when magnified, and those which do not. Kölliker, however, says this decided separation can no longer be maintained,[23] and he gives instances in proof of the connections that can be traced between the two forms. In the higher animals the striped muscles are the special instruments of will, and of movements that follow, or are accompanied by, distinct sensations. Striped fibre must be regarded as the highest form; and as a muscle of this sort contracts in length it increases uniformly in breadth.
[23] 'Manual of Human Microscopic Anatomy,' p. 63.
There are many other genera and species of fresh-water polyzoa besides the Plumatella repens, and they are found attached to sticks, stones, or leaves, generally to the under surface of the latter. They are all objects of great interest and beauty, which, whatever their diversity, conform sufficiently to one type that the student who has observed one, will easily recognise the zoological position of another. They should be viewed by transmitted and by dark-ground illumination, which produces very beautiful effects. To observe them in the performance of their functions, they require more room than the live-box can afford, but are well shown in the glass trough, whose moveable diaphragm enables them to be brought near enough to the object-glass, for the use of a power of about sixty linear for general purposes, and of from one to two hundred for the examination of particular parts. For a more detailed examination dissection must be employed, but all that we have mentioned can be seen without injury to the living animal, if specimens are kept till new cells are formed in water, which does not contain enough dirt to render their integuments opaque.
CHAPTER XII.
DECEMBER.
Microscopic Hunting in Winter—Water-bears, or Tardigrada—Their comical behaviour—Mode of viewing them—Singular gizzard—A compressorium—Achromatic condenser—Mouth of the Water-bear—Water-bears' exposure to heat—Soluble albumen—Physiological and chemical reasons why they are not killed by heating and drying—The Trachelius ovum—Mode of swimming—Method of viewing—By dark-ground illumination—Curious digestive tube with branches—Multiplication by division—Change of form immediately following this process—Subsequent appearances.
