28 



HARDWICKE'S SCIENCE-GOSSIP. 



Its eye is large and of bright red colour, and is 

 situated a short distance down from the mouth, and 

 just above the mastax. 



The water vascular organs are conspicuous. The 



Fig. 13. — Ertemias tctrathrlx. 



tortuous tubes, with vibratile tags (three on each 

 side), are distinctly discernible with a power of 500 

 diameters. The contractile vesicle is large, and 

 situated below the digestive organs, at the contracted 

 posterior end^of the lorica. 



It was in August, 18S5, that I had the good fortune 

 to discover this remarkable creature in Stormont 

 Loch, Blairgowrie. On examining a fragment of 

 milfoil, which I had dredged from the bottom of the 

 loch, in a zoophyte trough, with the water, I 

 observed the E. tetrathrix busy nibbling at a colony 

 stock of Codosiga umbel hit a. This beautifully 

 pedicled and collared Flagellata, as well as a number 

 of other forms of Pedicled Infusorians were thickly 

 attached to the leaves of the milfoil, which seemed to 

 form the chief article of food of the E. tetrathrix. 

 It did not leave the colony of C. iimbellata until it 

 had eaten most of the zooids from their foot-stalks, then 

 left the colony stock a complete wreck, to attack a 

 fine specimen of Acineta grandis. But the zooid 

 quickly retired to the bottom of its cup-shaped lorica, 

 and there baffled the efforts of the E. tetrathrix to 

 extract it, which left the A. grandis little the worse 

 for the assault. 



Its manner of swimming is unique. It swims quite 

 as easily and gracefully backwards as forwards. It is 

 the only species of the whole Rotifera I have met 

 with that can voluntarily reverse its motion. 



It will swim forwards amongst the leaves of the 

 plants and confervoid filaments, then shift its quarters 

 by swimming backwards quite as swiftly as by the 

 forward motion. I have seen many examples of this 

 creature, both in the summer of 1885 and 1886. 

 This voluntary reversing of the motion was a phe- 

 nomenon in every individual specimen. 



Its egg is oblong, and after extrusion is fixed by a 

 gelatinous matter to the posterior of the lorica on the 

 ventral side, and there carried until hatched. 



Length from tip of the centre frontal bristle to the 

 tip of posterior bristle, ^ of an inch. Length of 

 lorica, ^ of an inch. 



John Hood, F.R.M.S. 



Dundee. 



SECTION-CUTTING. 



THE following remarks, supplementary to Mr. 

 Underbill's admirable paper in the last issue, 

 may be of some interest. In preparing specimens 

 for mounting, the guiding principle in all the 

 necessary manipulations should be to avoid any 

 sudden change of density. For instance, it would 

 not do to transfer such delicate tissue as that of a 

 Medusa from 30 per cent, alcohol to 70 per cent, 

 without first placing it for a few minutes in 50 per 

 cent. As a rough rule, in passing a tissue which has 

 been treated with some such hardening substance as 

 corrosive sublimate up from water to absolute alcohol, 

 the strength of the solution should be increased 10 

 per cent, each time, and the substance should average 

 ten minutes in each, the time being slightly longer in 

 the earlier stages. Corrosive sublimate is by far the 

 best agent for first killing or fixing specimens, which 



