150 Mi see Han eo us . 



opened and the glass circle carefully examined ; others were allowed 

 to remain two days, three days, or for periods of weeks. 



In twenty-four hours it was found that a film had been left upon 

 the circle ; in forty-eight hours this film was plainly stony. The 

 earliest traces of this film, when treated with colouring-reagents, 

 stain ; but when treated with acids show no traces of lime nor any 

 evidences of structure; it is simply a structureless membrane. Later 

 films, when treated with acetic acid, present the appearance of a 

 tessellated pavement, and when examined with the polariscope 

 and not treated with acetic acid show beautifully the presence of 

 lime. 



It would thus appear that the epithelium of the mantle pours out 

 a secretion of horny matter, which forms the epidermis, that this 

 secretion holds lime in solution, and that from this the stony in- 

 ternal portion of the shell is formed. Experiments were successfully 

 made upon the shells of the oyster and Pinna and several other 

 lamellibranchs ; and some gasteropods were tried, but thus far 

 in vain. — Johns Hopkins University Circulars, November 1882, 



p. 7. 



Lantern-slides for Biological Lectures. 



Many of those who are engaged in lecturing to large classes and 

 to popular audiences on the elementary facts of biological science 

 have felt the want of a good series of lantern illustrations, which 

 should enable them to some extent to dispense with the large and 

 expensive diagrams that are now so generally used. 



A large series of this kind, illustrating all the more important 

 physical experiments, has been issued by Messrs. F. York and Son, 

 87 Lancaster Road, dotting Hill, AV. ; and arrangements have now 

 been made with the same firm for bringing out a biological series 

 under the supervision of Dr. Andrew Wilson and Mr. William Lant 

 Carpenter. It will contain illustrations of typical examples, with 

 the life-histories when possible, of the lowest forms of animal and 

 vegetable life (especially of those bearing on the Germ Theory), the 

 various classes of the Protozoa, the Coralligena, Echinoderms, Mol- 

 lusca, and Entozoa, the different phases of insect life, and the ele- 

 mentary facts of vegetable physiology. An excellent series illus- 

 trating human anatomy and physiology is already in existence ; and 

 there is also a little-known German series of zoological slides, which 

 is far less extensive, however, than that which it is proposed to 

 issue. Fossil forms will be illustrated in their proper places with 

 respect to living ones ; and preference will be given to the illustra- 

 tion of a few well-selected types rather than to minute differences 

 of detail. 



It is hoped that the knowledge that such a series is in prepara- 

 tion (for issue in August or September) may save the construction 

 of some diagrams, and may also induce those interested in the sub- 

 ject to suggest good figures suitable for photographic reduction. 



