1888.] MICEOSCOPICAL JOUKNAL. 137 



smallest diaphragm with which the condenser is supplied. By using a diaphragm below 

 the condenser its image and the object can be brought into focus at the same time. 

 Focus on the object, and then rack up the condenser until the diaphragm is clearly 

 seen. Then, when you remove the i^' and replace the jV^^. V^^ "'i^l ^rid that the lat- 

 ter has the light central, and can be used for the examination of any object requiring 

 central light with this objective. The difference between the illumination with the 

 plane or concave mirror alone and that with the achromatic condenser was next shown 

 by the effect upon a scale of Podnra pliimbca. With the condenser the light could be 

 much more easily modified, while at the same time it was kept central and the mark- 

 ings much more clearly defined. 



The advantage of using small diaphragms instead of large ones with the Abbe con- 

 denser was next shown, the object viewed being an Arac/moidisciis Ehrcnbcrgii. 



Wenham's reflex illuminator was also shown in the resolution oi AnipJi. pelluc. with 

 aBausch &Lomb ^s'^ homogeneous immersion objective and X^' eye-piece, magnifying 

 3200 diameters ; also with ],i" eye-piece (6400 diameters). This gives more light than 

 any other oblique illuminator, and, when once mastered, is the quickest. 



Beck's vertical illuminator for high powers was next shown, but the result was not 

 quite so satisfactory as the other performances, Mr. Smith stating that in order to ob- 

 tain the best results the lens should be a wide-angled homogeneous immersion, the 

 object mounted dry on the cover-glass, and that a small movable diaphragm be used 

 to modify the light, the smaller the stop the better. The opening used in this instance 

 was i^" 



Dark field illumination was obtained with Zentmayer's form of the Abbe condenser, 

 the smallest stop being used. Mr. Smith considered this form of condenser the best 

 that he had ever seen, far surpassing the ordinary paraboloid in sharpness, amount of 

 light, etc. 



March 22, 1888. — Meeting held at the residence of Dr. \A'm. B. Berry, Montclair. 

 Dr. Chambers showed a bicuspid tooth capped with gold, and which had been ex- 

 tracted on account of an abscess forming in the jaw. Dr. Allan made some remarks 

 on the methods of capping teeth, and said it was important that the band around the 

 neck of the tooth should not reach too far down, as it was liable to produce inflamma- 

 tion in the peridentium. With permission of Dr. Chambers the tooth was broken, and 

 it was found that the pulp chamber had not been cleaned and filled. 



Dr. Berry showed a fine specimen of tattooed skin taken from the arm of a sailor. 

 Dr. Brown e.xhibited mounted specimens of chancre and chancroids, and Mr. Woolman 

 presented some fine polariscope objects. 



NOTICES OF BOOKS. 



Observations on the Embryology of Insects and A?-ac/inids. By Adam Todd Bruce. 

 Baltimore, 1887. pp. 31 ; plates i-vi. 



The quarto volume before us is the Doctor's thesis, and its interest arises both from 

 the intrinsic value of its contents and because it is the last of the author's scientific 

 work. It contains a brief introductory sketch of Dr. W. K. Brooks, reviewing Dr. 

 Bruce's life and work, followed by the text of the thesis itself. The forms studied to 

 furnish a basis for the paper were Thyridoptcryx, C/uysopa, Mc/oc, Mantis a.nd. Musca, 

 and an undetermined spider. The results of the embryological studies for the general 

 classification of tracheates are briefly as follows : — Peripatus and myriapods from the 

 absence of wings may be regarded as very primitive members of the group ; peripa- 

 tus and the spiders are similar in the mode of origin of the germinal layers, but this alone 

 does not indicate close relationship ; embryological characters not alone sufficient to 

 separate the arthropod phylum. Arachnids with Limulus must be regarded as a dis- 

 tinct group because of the entire absence of antennae ; the antennas of insects and 

 Crustacea are probably homologous structures ; the amnion of insects and arachnids are 

 homologous and ally those groups ; the insects thus stand between Crustacea and 

 arachnids, and the three groups are none derived from the other, but more likely all 

 are from a common source ; the tracheae of insects and spiders are probably analogous 

 and not homologous structures. 



From this summary of the results of Dr. Bruce's work the reader can see that a 

 worker of no small promise was lost in the death of its author. Additions of perma- 



