ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 1083 



Weight, L. — The Optical Lantern. 



[Keply to " Kector," ante, p. 891. Waste heat cannot be utilized. As to 

 Newton's new improved 6 in. and ii in. objectives for the oil-lautern.] 



'Unjl. Mech., XLII. (1885) pp. 121-2. 



Wtthe, J. H. — The Microscopist ; a Compendium of Microscopic Science; 



including the use of the Microscope ; mounting and preserving microscopic 



objects ; the Microscope in Chemistry, Biology, Histology, Botany, Geology, 



Pathology, &c. 



4th ed., pp. i.-xii. 17-434, 240 figs, and 27 pis., Svo, Philadelphia, 1883. 



j8. Collecting', Mounting and Examining Objects, &c. 



Preserving Eggs of Cephalopoda and preparing Blastoderms.* 

 — Mr. W. E. Hoyle finds that when the youog Cepbalopods have reached 

 a stage at which the rudiments of the arms are clearly visible it is 

 moderately easy, after a little j)ractice, to extricate them by making 

 an incision into the egg-membrane with a fine scalpel ; but previously 

 to this period they so nearly occupy the whole interior of the egg that 

 it is almost impossible to obtain them uninjured. A quantity of such 

 eggs he preserved whole by a method suggested by Dr. Jatta. The 

 strings of eggs are placed whole in a weak solution of chromic acid 

 (about 0*25 per cent.) for a few hours, and then in distilled water 

 for twenty-four hours, after which they are preserved in alcohol. The 

 embryos can then be extracted much more readily than when fresh. 



A number of blastoderms in process of segmentation were pre- 

 served according to a method proposed by Ussow. The egg, without 

 removal of the membranes, is placed in a 2 per cent, solution of 

 chromic acid fur two minutes, and then in distilled water to which a 

 little acetic acid (one drop to a watch-glassful) has been added, for 

 two minutes longer. If an incision be now made into the egg- 

 membrane the yolk flows away and the blastoderm remains ; if any 

 yolk still clings to it, it may be removed by pouring away the water 

 and adding more. The blastoderms thus prepared show, when ap- 

 propriately stained, fine karyokinetic figures. 



Treatment of the Eggs of the Spider.j — The eggs of the grass 

 Bpider (Ar/alena noevia) are deposited in cocoons attached to the 

 under side of loosened bark and other sheltered places. During tho 

 entire winter cocoons may be found with eggs in early stages of 

 development. The species thrives well in captivity, so that there is 

 no diflBculty in obtaining eggs freshly laid. 



For studying the egg in a living condition tho long-used method 

 of immersion in oil is, Mr. W. A. Locy thinks, excellent. Tho oil 

 should be perfectly clear and odourless. Tho external features can 

 be studied to bettor advantage by mounting the eggs in alcohol after 

 they have been freed from the chorion and stained. Another valuable 

 method for surface study consists in clearing the already stained egg 

 in clove oil. Tho thickness of the blastoderm is most easily deter- 

 mined in this way. 



The best method of hardening preparatory to sectioning is that 



* Nature, xxxii. (188.5) p. .50G (Report to Britisli Association), 

 t Amor. Natural., xix. (1885) i)p. 102-22. 



