ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 285 



powers, may thus be mapped out with all the details exhibited in their 

 relation to each other." 



Double Illumination for Insects Mounted without Pressure. — 

 Mr. E. T. Draper in the same article says, " For good artistic work the 

 importance of double illumination cannot be too urgently advocated. 

 Many beautiful objects are often unappreciated from deficiency or 

 inapplicability of the light used to exhibit them. It is never more 

 exemplified than in the combined use of the paraboloid reflector and 

 side speculum, with a class of objects lately introduced, of j)arts of 

 insects mounted in fluid without pressure, avoiding the disturbance of 

 the more delicate tissues. Many parts of such preparations are neces- 

 sarily opaque, which is rather an advantage from an art point of view, 

 as, by force of contrast, their density aids in giving a most beautiful 

 appearance to the more transparent structures ; nothing being crushed 

 or distorted, all is in situ. These preparations immediately awaken the 

 mind to the impossibility of properly seeing or revealing them by the 

 ordinary reflected light from the mirror. The head and adjoining parts 

 of the male wasp prepared in this way by Mr. Enoch is singularly fine, 

 and a case in point ; with the paraboloid beneath the stage, and the side 

 speculum above, a combination of form and colour is seen, of surpass- 

 ing beauty. The light from the speculum touches the opaque parts 

 with reflections revealing the most exquisite tints of a metallic appear- 

 ance, while the paraboloid beneath shows, in actual perspective, the 

 wonderful parts beyond in all their natural colour, and bathed in light." 



Professor E. Hitchcock also points out * that although insect pre- 

 parations "mounted without pressure" are mounted as transparent, 

 there will always be some parts which are more or less opaque, espe- 

 cially in the larger specimens, and he has found much benefit from the 

 use of a condensing lens above, as for an opaque object, at the same 

 time throwing in light from below. A specimen of Gimex mounted in 

 balsam by the carbolic acid process affords a good illustration of the 

 utility of this double illumination. 



Behrens' Guide to Microscopical Researches in Botanical La- 

 boratories.t — A collected summary of methods and processes in 

 botanical microscopy is much wanted, the literature on the subject 

 being more scattered than is the case with histological methods in 

 zoology. The author of this book has largely contributed to meet 

 this want by the compilation now published, though it is to be 

 regretted that the descriptions of Microscopes and apparatus occupy 

 so large a proportion of the work, the 4th and 5th sections — the 

 pieces de resistance of the book — being limited to pp. 219-387, 



There are five sections: — 1. General Description of the Micro- 

 scope (pp. 1-75). 2. Accessory Apparatus (pp. 76-129, Dissecting 

 Microscope, Camerae, Micrometers, Polarizers, Goniometers, and 

 Microspectroscopes). 3. Preparation (pp. 130-218). 4. Microscopical 

 Reagents (pp. 219-61) ; and 5. Microscopical Investigation of the 



* Amer. Mon. Micr. Journ., iii. (1882) p. 219. 



t Behrens, W., ' Hilfsbuch zur Ausfiihrung mikroskopischer Untersuchungen 

 im Botaiiischen Laboratorium.' xii. and 398 pp., 132 figs, and 2 plates. 8vo, 

 Braunschweig, 1883. 



