25 
lowered gradually parallel to the stage, and the object is 
proportionally compressed ; the inner part of plate (H, N) is 
bevelled off, to enable the observer to follow the object to a 
considerable degree, should it be inclined to slip from under 
view. When the compression is ended the milled head (P) is 
worked back to raise the compressing plate clear of the slide, 
and the compressor can be again turned aside on releasing the 
catch with the finger at K. 
I have found this instrument particularly useful in the 
examination of Entromostraca, which are fragile, and if 
injured obscure the view, also in researches on Rhizopoda 
and Rotatoria ; in fact, in almost every department of micro- 
scopic work it will save a vast amount of trouble, and, I trust, 
mect with the approbation of microscopists. ‘The compres- 
sorium represented in these diagrams has been beautifully 
constructed by Mr. ‘Thomas Ross, of London. 
Nores on AMPHIDOTUS cCoRDATUS (Penn). 
By Davin Rosertsoy, F.G.S.! 
In the early part of 1868, on the shores at Cumbrae, my 
attention was attracted to many holes occurring in the sand. 
In tracing them to a depth of four or five inches, I found an 
Amphidotus cordatus under each hole. The diameter of the 
hole was about equal to that of a crowquill, and often irre- 
cular, and rose straight over the long spines surrounding the 
dorsal impression of the test. By placing one of the animals 
in a glass jar with two or three inches of sand below and 
over it, and covering the whole with water, an opportunity 
was afforded of seeing how the holes were produced and kept 
open. Long contractile processes, with tentaculated heads— 
described by Forbes as “long ringed worm-like suckers,” 
and by John Johannes Miiller as ‘‘ locomotive feet’’—were 
thrust up through the sand, and were seen slowly, and appa- 
rently searchingly, wandering over its surface, then grasping 
particles of the sandy matter in their tentacles, and finally 
dragging them rapidly down into the hole. As these holes 
extend from four to five inches into the sand, and I have 
seen these prehensile tentacles stretch between two and three 
inches over its surface, the length of these instruments cannot 
be less than six or seven inches. 
1 Communicated by Dr. Anthon Dohrn, of Jena. 
