556 Clironicles of Science. [Oct., 



induction currents : — 1. The time elapsed between the closing or 

 the rupture of the circuit and the apparition of the current of 

 induction, or the attraction of the armature for the "bobbin of induc- 

 tion, is inarjpreoiable, being less than the fiftieth part of .a second. 

 2. The current of induction, feeble at its commencement, lucres 

 little by little, then diminishes, and is extinguished in an interval 

 difficult to determine. 



All who have experimented much at electrotyping have been 

 troubled by a defect in the electro deposition of copper, which is 

 sometimes seriously injurious, viz. its brittleness. M. Bouillet has 

 found that a very small quantity of gelatin dissolved in the bath 

 gives a copper of nearly equal malleability to rolled copper, whereas 

 the pure bath only .gives a porous, defective metal-like cast copper. 

 The relative specific gravities of copper in different states are : cast 

 copper. S-78 ; laminated copper, 8*95 ; galvanic copper, 8*86. 



Gutta-percha moulds are exclusively used by the large firm of 

 Christophle and Co., Paris. They are applied either cold by 

 pressure with a lever, or by the hand. The mould is rend 

 conductive either by blacklead, or silver, reduced from the nitrate by 

 nascent hydrogen. 



10. ZOOLOGY, ANIMAL PHYSIOLOGY, AST) 

 MORPHOLOGY. 



MOKPHOLOGY. 



Occluding Apparatus of the Trachea in Insects. — Burmeister was 

 the first who showed that insects have a means of closing up their 

 tracheae so as to prevent all communication with the exterior. The 

 subject has since been studied by Herman and Leonard Landois, 

 and by "W. Thelen. They have found an apparatus adapted for 

 this purpose in all insects, consisting of an imperfect chitinous 

 ring (a muscle) ligament, and sometimes an accessory \e 

 Such an apparatus is placed in each main tracheal stem Mow, and 

 independent of the stigma. Dr. H. Landois and W. Thelen have 

 recently published a joint memoir on the subject. The complex 

 of development of this apparatus they show varies very much in 

 different orders of insects, and i l the Neuroptera is reduced to a 

 minimum. In many cases it is so much developed, as to constitute 

 a sort of larynx, and as such may serve as a vocal organ. The 

 solid chitinous parts are always connected in such a way, that in a 

 state of quiescence the tracheal tube remains open, and gives free 

 entrance and exit to the air through the stigma. Muscular action 

 is necessary to close the apparatus. This is effected in all cases by 



