442 
POPULAR SCIENCE REVIEW. 
with the same objective ; and the fourth contains two photos, one a large 
one representing the 19th band of the 19 plate-band, magnified 1,100 with 
Powell and Lealand’s ^th immersion, and the smaller an enlargement of 
part of the other to 2,750 diameters. 
Synchceta under the Microscope . — Dr. Hudson, in a recent article on this 
subject, in the Monthly Microscopical Journal, says that when once Syn- 
chceta is placed between two plates of glass in a drop of water sufficiently 
small to keep it within the field and tolerably within the focal length even 
of an inch objective, its characteristic motions cease ; it swims incessantly 
round and across its prison, and at such a rate that the eye gets weary of 
following it. By gently compressing it one good view can be obtained, but 
then it is always the same, or at all events can be only slightly altered by 
reversing the compressorium. In consequence of this no attempt has been 
hitherto made to describe the top of the head, or to delineate the front or 
side view. Its outline when swimming with either dorsal or ventral surface 
at right angles to the line of sight is that of a boy’s kite ; and exactly 
where the kite’s tassels would be are two movable lobes fringed with a 
ring of powerful cilia, by means of which the creature performs its various 
antics in the water. Though the cause of ciliary action seems to be a 
mystery, yet the various ways in which the cilia of the lobes must work to 
produce Synchceta's motions admit, he thinks, of being explained. 
The Anatomy of the Chiton. — In the Archives neerlandaises (t. iv.) M. W. 
Marshall gives an interesting account of the above. He describes the tests 
as composed of two parts, covered with an epidermis : the articulament and 
the segment. The former is composed of four layers ; the deepest of these 
consists of calcareous prisms placed perpendicularly to the axis of the animal, 
and further it presents the several zones having different degrees of colour ; 
the second layer is harder and thicker, and is composed simply of very fine 
granules, it is porcellanous, translucent, and of a bluish-white colour; the 
third layer is, like the first, composed of prisms placed at right angles to the 
axis, viewed in section they have the appearance of being finely striated ; 
the upper layer is of a very peculiar nature. The author says that each 
articulus buccalis is seen to consist of ten peculiar triangular bodies whose 
points converge to form the point of the articulus. Each of these triangles 
in its turn appears to be formed of a number of needles, so arranged that 
they help to give the triangular shape to the body, and are themselves con- 
stituted like a feather of a shaft and minute crystalline barbs, and possibly 
barbules. M. Marshall gives a series of figures depicting these singular 
structures, and in fact enters into so many details as to render it impossible 
for us to give a just abstract of his views. 
Microscopic Illumination. Mr. Wenham and Dr. Piyott. — The result of 
the present controversy is at present undecided. Whether Mr. Wenham or 
Dr. Pigott is right remains we think to be proved. Dr. Pigott is certainly 
gaining ground, but then the question may be asked, Is not this because 
Mr. Wenham is remaining quiet? We cannot venture to say on whose side 
right lies, but the following quotation from a paper by Mr. Wenham may 
be of interest. “ It is scarcely to be expected,” says Mr. Wenham, “ that 
those who have not in some degree been practically familiar with the con- 
struction of object-glasses, can be fully aware of the value of the mercury 
