184 Recent Literature. 



aquatic conditions in which they were born (phylogenetically), and 

 which they must preserve or lose their auditory organ completely." 

 He believes that the cochlear organs alone are enabled to perceive 

 all kinds of sound. The sound waves institute a responsive vibra- 

 tion in all or nearly all the filaments, in succession, of the hair-band 

 of the organ of Corti, according to Mr. Ayers. " Timbre, or the 

 tonal color of sounds, is due to a combination of the stimuli or the 

 effects of the excitation of a series of vibrations of which the main 

 or fundamental tone is most prominent, while the other vibrational 

 impulses make themselves felt as 'coloring' of this base. The 

 combination is a psychical phenomenon, and there is no combined 

 result of simultaneous sympathetic vibrations transmitted from the 

 ear; on the contrary, each vibrational impulse is transmitted to the 

 brain at its full value, and its effect in audition is due entirely to 

 psychical processes." C.a.k. 



Psyche, February, 1892, contains a contribution on the " Blood- 

 tissue " of the insecta by William M. Wheeler, continued in 

 the March and April numbers. The papers give evidence of very 

 careful and thorough work in a comparatively unworked field. 



C.A.K. 



The Nature of the Shoulder Girdle and Clavicular Arch in Sau- 

 ropterygia. By H. G. Seeley. Proc. Roy. Soc. li, pp. 119-151. 

 A comprehensive investigation of the clavicular arch in Plesiosauridae 

 and Elasmosauridse, with a scheme of classification for the two groups. 

 In discussing the classification, the author cites facts illustrative of 

 Cope's law of parallelism. He says: "And it is remarkable that 

 many Liassic species have the articular faces of the vertebral centra 

 deeply biconcave, while in many Cretaceous species those surfaces 

 are nearly or quite flat; in the shoulder girdle nothing but continued 

 ossification, apparently, is needed to convert the Liassic Plesiosaurian 

 into the Oolitic and Cretaceous Elasmosaurian type. Eretmosaurus 

 is the nearest approach to this type known from the Lias. 



It thus appears as though some animals complete their embryol- 

 ogy early in life, others at intervals during life, while in most types 

 the embryonic development takes place gradually during successive 

 epochs of geological time, giving rise to classification of its stages, 

 indicated as genera, families, orders; and, therefore, that the young 

 individuals of a late period of time simulate genera of an earlier 

 age." C.A.K. 



