NOTES AND MEMORANDA. 
199 
arrangement, and is clamped at the back of the instrument by a strong 
screw and nut. This stage can be readily removed from the instrument 
and replaced by any other form of object support to suit the special 
requirements of microscopists. 
The idea of swinging the sub-stage and illuminators on the line of 
the object under observation is not a new one, several plans having 
been adopted from time to time by different microscopists to effect this. 
The most important was the subject of a patent more than twenty 
years ago, by Mr. Grubb, of Dublin, who fixed, exterior to the stage, a 
sector comprising nearly a semicircle, upon which the attachments 
for the illuminators were made to slide. The centre of the arc was 
set so as to be coincident with the object in focus on the stage. The 
Zentmayer system, however, of swinging the sub-stage is the most 
simple yet devised, and does not interfere with the stability or ordi- 
nary use of the instrument, for when the swinging bar is clamped in 
line the peculiarity at first sight is not readily observed, and the 
contrivance of this effective arrangement is very creditable to the 
ingenuity of Mr. Zentmayer. 
Digestive A'pgmratus of Spiders. — M. F. Plateau has communicated 
papers on this subject to the Academie Eoyale of Belgium, in whose 
‘ Transactions ’ they will be found, and in the ‘ Bulletin of the Societe 
Beige de Microscopie,’ January 31, 1878. He states that the di- 
pneumonous spiders have the pharynx and oesophagus so narrow, that 
the juices of their prey penetrate the buccal intestine by capillarity ; 
the dilatation of the suction organ driving them forward. When this 
organ contracts, the narrowness of the tube obstructs their return 
like a cork, and they are propelled into the middle intestine. In 
the first part of their course they are mixed with the pharyngeal 
secretion, which may have the properties of insect saliva, but no ex- 
periments have been made with it. From a mechanical point of view, 
the c9Bca of the middle cephalo-thoracic intestine only play a passive 
part ; and if they serve as reservoirs, the liquids only enter them by 
the pressure occasioned by the suction organ. The csecal secretion is 
not acid, and probably not analogous to gastric juice. It is an error 
to suppose the middle cephalo-thoracic intestine of spiders is analogous 
to the stomach of vertebrates. The principal digestion of albuminous, 
starchy, and fatty matter is effected by the energetic action of the 
liquid specially secreted by the abdominal gland, which is generally 
yellow, and containing fine granules, fat-globules, and epithelial cells, 
more or less intact. It is slightly acid. As with insects and decapod 
crustaceans, the acting ferment is evidently different from the pepsine 
of vertebrates, and an addition of a feeble trace of hydrochloric acid, 
instead of enlivening its action, completely stops it; but, like the 
pancreatic juice of vertebrates, certain salts, such as carbonate of 
soda, slightly promote it. This liquid raj^iclly transforms starch into 
glucose. The abdominal gland of the spider is not a liver, although 
its containing glycogen, together with its form, tend to the siqqm- 
sition. Its liquid does not exhibit the pro2)ertics of bile, nor its 
colour with reagents. It rather resembles the pancreas of vertebrates, 
but the likeness is not perfect. The matters accumulating in the middle 
