SELECTED NOTES. 827 



days, the skin became very clear and transparent. I laid them to 

 dry upon the slide with another slide over them, and afterwards 

 mounted in balsam. Though some of the anchors were broken, 

 some on each piece of skin were quite perfect. By soaking longer 

 the skin dissolves and the anchors and plates fall to the bottom. 

 The sediment baffled me, but am told that if I had then used 

 some rectified spirit the fatty matter would have been got rid of 



John P. Hall. 



Ditto. — Before placing to dry between glass slips, the softened 

 skin of the synapta should have been put between pieces of paper. 

 This would have prevented their sticking to the glass and subse- 

 quent breakage. A. 



Spinal Cord. — This, as most persons know, extends from the 

 brain to the lower part of the spine, and is the medium of com- 

 munication between the nerves and the brain. It lies in a kind of 

 tunnel, formed by the successive arches of the vertebrse placed in 

 apposition to each other. I once met an advanced (I) student who 

 did not know how the cord was situated. It is enclosed, as is the 

 brain also, in three membranes. The innermost is excessively 

 delicate, and is called //<s; mater (that is, " dutiful mother." This 

 fanciful name, or, rather, its Arabian equivalent, was given it by 

 the Arabians or other Eastern physicians, because of the persist- 

 ency or affection with which it clings to the brain and cord). 

 Next to the pia mater lies the middle membrane, called Arachnoid 

 (that is, " Spider's web-like "). The outermost is called Dura 

 mater (that is, " hard mother '"). This is a stout and firm mem- 

 brane, and probably escapes from the razor when one attempts to 

 cut a section of it ; at all events, it appears to be missing from the 

 section before us. F. J. Allen, 



Tentacle of Physalia palagica (PI. XIII. , Figs. 5 — 8), com- 

 monly known as the " Portuguese man-of-war.'' This specimen 

 was given me by Captain Mortimer. The tentacles are from 

 twenty to thirty feet in length, and consist of a muscular band, 

 studded on its margin by a double row of beads, each bead being 

 a mass of minute spherical cells, and each cell containing a spiral 

 stinging-thread, coiled up cork-screw fashion, inside. Captain 

 Mortimer, who is a distinguished naturalist, found the animal from 

 which this was taken in the Pacific Ocean by surface-dredging. 

 He had frequently witnessed the discharge of the stinging-threads 

 from the cells, and stated that their stinging power was perceptible 

 for some days after the death of the animal. J. C. Thompson. 



