184 Peecent 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,”’ Ci dates 
_ 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. 
CA 
The Nature of the Shoulder Girdle and Clavicular Arch in Sau- 
roplerygia. By H.G. SEELEY. Proc. Roy. Soc. 11, pp. I19g-I5I. 
_A comprehensive investigation of the clavicular arch in Plesiosauridee 
and Elasmosauridz, 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. Lretmosaurus 
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 
: ” 
oe C.A.K. 
