910 General Notes. [November, 



By using other shapes of pierced cardboard and employing a 

 spy-glass with two objectives separated by a bi-refringent prism, 

 and provided with a graduated arc, the degree of astigmatism of 

 the cornea can be calculated, but that of the crystalline can only 

 be obtained by subtraction from the total astigmatism, which 

 must be obtained by another and less precise method. 



W. Leche upon the Milk Dentition and Homologies of 

 the Teeth of the Cheiroptera.— The species the milk dentiti< 



of which was examined were Vespert \,> p \ a n a and V. Dauben- 

 tonii; Vesperugo Nathusii and V. no tula; Vcs^crus serotinus, V. 

 borealis, and V. velatus; Plecotus auritus, Sturnira lilium, and 

 Rhinolophus hipposlderos. In all the Vespertiliones the formula 

 was: i. \z^, c. J— I, m. 2 2 -]; m Sturnira the third incisor of the lower 

 jaw was wanting ; while in Rhinolophus the only milk-teeth that 

 could with certainty be found were : c. l j\ m. tl 



In Rhinolophus the milk-teeth never break through the jaw; 

 but remain concealed until their entire resorption. 



In the other species the milk-teeth lie in more or less perfect 

 alveoli upon the outer border of the jaws, outside and behind the 

 developing permanent teeth. At a certain stage of development 

 almost the entire set of milk-teeth can be found exterior to the 

 nearly complete set of permanent ones, a singularity rendered 

 possible by the small size and simple form of the permanent 

 teeth. As many as 50 teeth may be found in nearly adult indi- 

 viduals. The milk-teeth have their crowns covered with enamel 

 and always more or less three-lobed (the two outer lobes in some 

 cases rudimentary), with the tips of the lobes hook-like and 

 directed inwards and backwards. The root, always the greater 

 portion of the entire length, is single, the second milk-incisor of 

 Plauritas excepted. 



The milk-teeth resemble each other greatly in each individual 

 and throughout the tribe, instead of, as in other mammals, exhib- 

 iting characters similar -to those of the second set. Our author 

 considers, therefore, that both sets are typical, the first exhibiting 

 the type of the homodont mammals, the second the higher type 

 of the heterodont mammals. The permanent incisors are usually 

 equal in number to the milk incisors, but in Dysopes they are tS 

 against -13; while in Desmodus the four upper milk-incisors are 

 replaced by two enormous teeth which have not the remotest 

 resemblance to their predecessors. From the position of the 

 milk-molars with regard to the permanent ones, the following is 

 the formula of the second. Vespertiiio p.m. lm.\; Plecotus p. 

 m. I m. 1; Vesperugo p.m. \ m. \ ; Vesperus p.m. \ m. J ; the re- 

 duction invariably taking place first in the upper jaw, instead ot 

 of in the lower, as usuaf in mammals. In some other genera the 

 molars also are reduced, exhibiting in the Stenodermata a series 

 commencing with Brachyphylla and Sturnira with m. I, and end- 

 ing with Desmodus with {, 



