October 25, 1895.] 



SCIENCE. 



5G3 



the periphery ; on the field of regard ; the fit- 

 ness of the form and place of the retina for the 

 production of a distinct image; the power of 

 dispersion by the eye for different colors. Fin- 

 ally he takes up the famous problems of the me- 

 chanism which produces accommodation. To 

 produce a distinct image of a given object on a 

 screen the lens must be placed at a certain fixed 

 distance from the object ; bow is it then that the 

 screen known as our retina is able to receive 

 distinct images at different distances? This 

 problem is one not yet solved in all its complex- 

 ity. The explanation offered by M. Tschern- 

 ing is that the alteration required in the crys- 

 talline to form an image of objects near by is 

 produced by the tension of the borders of the 

 crystalline, thvis increasing the convexity of the 

 center. This is also Young's idea. Helmholtz 

 sought to explain the alteration of the crystal- 

 line by an entirely different mechanism. Be- 

 fore entering upon the subject Young under- 

 takes to eliminate the various other causes which 

 might be invoked in elucidation of the problem. 

 To prove that the cornea bears no part in ac- 

 commodation, he neutralizes its refracting power 

 by immersing it in water and substituting in its 

 place a lens, and observes that there is no 

 change in the range of his accommodation. One 

 cannot but be struck with admiration for the pa- 

 tience and ingenuity which such an operation 

 supposes. The decisive argument in favor of a 

 change of form in the crystalline is derived by 

 Young from a fact which Wollastan and Helm- 

 holtz sought in vain to verify, but which is veri- 

 fiable on the eyes of youth, i. e. , the correction 

 of the aberration during accommodation. His 

 determination of the nature of crystalline altera- 

 tion was due to another fact which has just re- 

 cently been verified — that the capacity of ac- 

 commodation is half as much again greater at 

 the center of the crystalline than at its pe- 

 riphery ; from which he concluded a flattening 

 of the surfaces at the periphery. 



It will be seen by this brief review to what 

 an extent the ideas of Young on ophthalmology 

 are still fresh and of absorbing interest ; more 

 than any other he has prepared the way for the 

 final solution of these problems. 



Charles Heney. 

 Paris. 



SOCIETIES AND ACADEMIES. 

 THE ENTOMOLOGICAL SOCIETY OF WASHINGTON. 



The 110th regular meeting was held October 

 10, 1895. 



Mr. Hubbard read a paper entitled ' Addi- 

 tional Notes upon the Insect Guests of the 

 Florida Land Tortoise,' in which he gave his 

 observations of the past summer, including a 

 number of facts supplemental to his article on 

 this subject published in Insect Life, Vol. VI., 

 No. 4. The list of regular inhabitants of the 

 burrows of the Florida laud tortoise now reaches 

 19 species, of which 18 are insects and one is a 

 vertebrate {Bana cesopus). Aside from these, 5 

 insects are constant visitors to the burrows. The 

 paper was briefly discussed by Messrs. Sohwarz 

 and Gill. Mr. Schwarz referred to the possible 

 finding of a similar insect fauna in the burrows of 

 the European Testudos and of the two other 

 American species of Gopherus. Dr. Gill showed 

 that the European species do not make burrows, 

 and argued that in spite of the close resem- 

 blance of American forms to the Florida species 

 we must not necessarily assume that they are 

 burrowers. Mr. Schwarz said that the inhabi- 

 tants at Penas, a station on the Mexican Na- 

 tional Railway, near Laredo, informed him that 

 there is a burrowing tortoise in the great sand 

 plains near that place. This he thinks may be 

 G. herlandieri. 



Mr. O. F. Cook made some general remarks 

 under the head ' Insect Collecting in Africa, ' 

 describing some of the rarities which he had 

 found, giving in some detail his impression of 

 the insect fauna of Liberia, and describing his 

 experience with driver ants. These insects, he 

 thinks, may be responsible for the almost total 

 absence of snakes in Liberia, since when snakes 

 are gorged with food they are motionless and 

 defenseless and are easy prey for these active 

 and voracious ants. Mr. Schwarz remarked 

 that no trace of a more or less permanent nest 

 of Eciton has ever been found, and the queen is 

 not known. These ants make temporary nests 

 and are in the main peripatetic. The fact that 

 we do not know the queen, however, argues 

 that a true nest will some day be found. He 

 called attention to the fact that the Rev. P. 

 Jerome Schmidt has found a species of Eciton 

 in North Carolina. 



