318 General Notes. [ March, 
gins of the larval valves, lined with ectoblast (mantle), into which 
the vent opens. e anterior adductor muscle degenerates after 
fixation, when its function is assumed by the posterior adductor, 
which develops after the former. The cephalic ganglion origi- 
nates from an epiblastic thickening situated in the center of the 
- trochal disk or velum. e larval shell is homogeneous; but at 
the hinge there are two small teeth separated by an interval from 
each other. 
The earlier stages are copied from Mobius, who incorrectly 
represents the nucleolus of the ripe egg as being spheroidal, 
whereas the writer has shown it to be a double body in the ova 
of the three species, including O. edulis, investigated by him.) 
Dr. Horst’s more recent investigations upon the early growth 
and fixation of the fry or veliger stage of O. edulis and its meta- 
morphosis into the “spat” are of great and significant interest. 
Carrying out more fully a suggestion made by the writer in 1881, 
Dr. Horst used a wooden frame, into which could be fixed a large 
number of glass slides, such as are used by microscopists. This 
frame, with its contained slides, some of which were coated with 
hydraulic cement, was immersed for a period of seventy-two 
hours in waters where free-swimming oyster larva were known to 
exist, at the end of which time spat was found adhering to the 
slides, measuring 0.24™" in height (q}+ of an inch). After fixa- 
tion, which seems to occur in the same way as in the American 
species, the permanent shell is formed or built up by the mantle 
beyond the margins of the valves of the fry, a homogeneous 
membrane, subdivided internally into polygonal spaces or areas, 
being first laid down by the mantle border. In these prismatic 
areas of the periostracum, calcification occurs by the deposit of 
calcic carbonate, and the shell is thus moulded upon the mem- 
branous matrix of conchioline. Attachment and growth of the 
young edible oyster, according to Horst, is very similar to that ot 
the American species, as described by the writer (Bull. U. S. Fish 
Commission, ii, 1882, p. 383). The outgrowth of the first branchie 
as two series of distinct ciliated processes projecting into the 
mantle cavity of the spat is interesting as showing that the more 
primitive condition of the lamellibranchiate gill was much simpler 
than in the existing adult oyster. 
PHYSIOLOGY: 
__ Tue TEMPERATURE SeENsE.—By an ingenious device Dr. Pol- 
~ litzer has been able to make what are probably exact determina- 
~ tions of the sensitiveness to heat of the skin in different parts of 
__ the body. The rounded bottom of a small platinum cylinder was 
. = Bull. U. S. Fish Commission, 11, 1882, p. 213. 
~ >This department is edited by HENRY SEWALL, of Ann Arbor, Mich. 
sees ae 
