MANUALS, ANATOMY AND PHYSIOLOGY. Moll. 11 
Kobelt has published a further part of his “ Illustrirtes Conchy- 
lienbuch,” containing the end of the Stylommatophora, the Basornmato- 
phora {LitiinceidcB^ &c.), Solenoconchce, and a part of the Bivalves. 
Anatomy and Physiology. 
1 . General Morphology. 
J. W. Spengel essays to prove the derivation of the asymmetry in the 
intestines of many Gastropods, chiefly the Prosohranchia (M. E.), from a 
torsion of the hinder part of the originally symmetrical body, by which 
the heart is turned round, its anterior end with the origin of the aorta 
becoming posterior, its left auricle right-hand, the left gill right, and 
vice versa ; the visceral nerves were originally also symmetrical, and their 
chief commissure at the hinder end of the body behind the heart and 
vent ; but by this torsion, the left chief branch of the visceral nerves was 
conducted across the median line below the intestine, the right above it, 
and their commissure advanced forwards above the aorta and intestine. 
This is considered to be the origin of the singular noose-like conforma- 
tion of the commissure which was pointed out first by H. v. Ihering in a 
part of those Mollusca [see Zool. Rec. xiii. Moll. p. 10]. The sym- 
metrical structure of the body which is most shown in Chiton and in the 
Bivalves, is therefore the more primitive, and the Pteropods, although 
they have some important points of resemblance to the Cephalopods 
G.g.j the cephalic cones), are essentially separated from them by the 
asymmetrical arrangement of their intestines. Z. wiss. Zool. xxxv. 
pp. 333-373, pi. xvii. 
W. Brooks thinks that the paired arms of the Cephalopods cannot be 
homologous to the single foot of the Gastropods, but are paired out- 
growths from the foot region ; the homology goes no farther than the 
parts of the yelk during the stage of segmentation. Am. J. Sci. (3) xx. 
pp. 288-291. 
2 . Muscular System and Movement. 
H. SiMROTH makes some general remarks on the locomotion of the 
Mollusca. The snails and the Turhellaria are the only animals which 
move by true gliding, the foot continually adhering to the bottom, not 
loosening and re-fixing itself step by step, but advancing by extension of 
the longitudinal muscles [c/. Zool. Rec. xvi. Moll. p. 13]. The same 
mechanism is employed by the freshwater snails, which creep and do not 
swim along the surface of water. Cyclas ascends vertical objects by 
fixing its shell by very fine byssus-threads, step by step. Z. ges. Naturw. 
(2) V. pp. 500-504. 
The presence of striated muscles in the adductors of the genus Pecten 
is stated by R. Blanchard, Rev. Int. Sci. 1880, No. 4, and by Con- 
stance, Bull. Soc. Brest, 1879. They are not found, according to 
Blanchard, in the adductors nor in any other part of Mytilus, Anodonta^ 
and Unio ; earlier statements by other authors concerniug them seem to 
be doubtful or wrong. Abstract in J. R. Micr. Soc. iii. p. 930. 
1880. , [voL. xvii.] B 9 
