382 Miscellaneous. 



accompanies the connective extended from the branchial ganglion to 

 one of the buccal ganglia during its passage through the gastro- 

 genital mass ; the object of this arrangement appears to be the pre- 

 vention of the dragging (tiraillement) of the nerve when the organ 

 is distended with eggs. 



Another remarkable arrangement is to be seen in the passage of 

 the last portion of the intestine through the heart. At the entrance 

 of the intestine into the ventricle there are muscular bundles starting 

 from the wall of the latter and inserted perpendicularly into the wall 

 of the digestive tube ; at the moment of contraction these bundles 

 must, by their shortening, tend to draw apart the walls of the intes- 

 tine, which would otherwise be compressed during the systole, and 

 thus the course of the faecal matters will not be interrupted. 



In these large mollusks the difference between the arteries and 

 veins is very easily seen : the former have a very distinct double 

 epithelial and fibrous wall, whilst the latter are simple sinuses hol- 

 lowed out in the tissues. All the blood is compelled to traverse an 

 organ of hsematosis (branchiae or mantle) before returning to the 

 heart. 



The proper temperature of the animal, compared with that of the 

 bottom at which it lives, appeared to be rather high. The tem- 

 perature registered by thermometers sunk at the point inhabited by 

 the animals was about 63° - 5 F. (17°'5 C.) ; the average temperature 

 of the Tridacnce was 68°- 5 F. (20° C.).—Com_ptes Rendus, Oct. 9, 

 1865, p. 601. 



Remarks on the Protective Sheath and on the Formation of the 

 Stem of the Root. By M. R. Caspary. 



In preceding memoirs M. Caspary has indicated a layer of very 

 closely approximated cells, placed in a single series in thickness, 

 which exists in stems, roots, and leaves, the vascular system of which 

 it envelopes and protects. He has given it the name of the protec- 

 tive sheath, although in certain cases (in Berberis, for example) 

 this layer is ruptured during growth, and consequently does not 

 serve to protect the organs which it envelopes. In describing this 

 protective sheath, M. Caspary indicated upon the lateral walls of its 

 cells some darker spots or streaks, which he thought were formed 

 by very small pores. He now again maintains the existence of 

 these spots or streaks ; but he has ascertained that they are due to 

 foldings of the walls of the cells, and not to pores. He has observed 

 these folds in the protective sheath of Ficaria ranunculoides, Roth, 

 Elodea canadensis, Mich., Brasena peltata, Peret, and Charlwoodia 

 rubra, Planch. When the cells of the protective sheath become 

 thickened, the folds gradually disappear. M. Caspary attributes 

 this change to the elongation of the walls of the cells — an elongation 

 of which he has convinced himself by direct measurements. 



Several authors (especially M. Karsten) have regarded this pro- 

 tective sheath as a lignified residue of the layer of cambium which 

 has produced the other parts of the stem ; but M. Caspary combats 



