Proceedings of Scientific Societies. 205 



Dr. Gray read a paper on the anatomy of the insect trachea, 

 largely made up of references to the early literature of the subject. 



July 1, 1891, C. W. Wood worth, of the Agricultural Experiment 

 Station at Berkeley, was present and exhibited some slides, showing 

 the scale insect infesting the leaves of the olive. He called attention 

 to the fact that certain closely allied species of scale insect were 

 invested with an outer covering produced by exuvia, or by harden- 

 ing of the skin, while in the species under consideration this outer 

 covering seemed almost entirely composed of the stellate hairs 

 accumulated from the under side of the leaf of the olive on which it 

 feeds. As the larva grows it insinuates itself beneath these stellate 

 hairs, which become broken from the leaf and attached to the skin 

 of the developing insect. Mr. Wood worth exhibited two slides last 

 evening, one the young larval skin, of about one-fourth the adult 

 size, and the other the complete adult form. 



Henry G. Hanks was present and exhibited some curious so- 

 called lava, recently obtained from Butte county. In November 

 last Air. Hanks read a paper before this society on 'Certain Mag- 

 netic Rocks,' in which he assumed that the rocks at Tucson were 

 nearly identical with the Table Mountain capping, which overlies 

 the deep good placers of this State, protecting them from denuda- 

 tion and dispersion. During a recent visit to Butte county for the 

 study of this formation he made two important discoveries bearing 

 on this subject, which at least afford strong evidence in favor of the 

 opinion stated in the paper referred to, that the rocks were not of 

 igneous, but of aqueous origin. 



The first discovery was at the mouth of Chico canyon, where 

 W T illiam Proud showed him some cylindrical natural tubes in the 

 so-called lava, which Mr. Hanks believes to be solfataric steam 

 pipes. These varied from the size of a quill to three inches or more. 

 and some of them are at least four feet deep. They are not rare, 

 but common, and it is believed may be found elsewhere. The infer- 

 ence drawn from this discovery is that these rocks, supposed to be 

 igneous, are really overflows of solfataric mud ; otherwise it would 

 be impossible to account for the steam pipes, for the rock must have 

 been at one time soft and permeable. 



The second discovery was a fragment of the same rock obtained 

 from Mrs. Caroline H. Church of the Aurora drift mine, near Maga- 

 lia, in which there is a cast of a pine cone, so perfect that when 

 liquid plaster of paris is poured in a model of a cone is obtained 

 showing every detail of structure. Mr Hanks has examined the 

 cast closely with the microscope, and could find no trace of charcoal. 

 Nor can it be possible that the rock was hot, for had the cone 



