A special volume would be required for anything like a complete examination of the little which is known on this subject, but these few remarks may assist the microscopic beginner in examining the movements of his subjects, and guard against the error of referring to reason and volition those which are, probably, either the direct result of stimulants applied to the surface (as in nerveless creatures), or the indirect (reflex) result of such stimulants in beings like the rotifers, who have a nervous system; or the result of _sensations_, which excite actions without previously referring the matter to the decision of a will. It must not, however, be too readily assumed that the behaviour of creatures possessing distinct organs is entirely automatic; and we must not forget that even the best physiologists know very little concerning the range of functions which the nervous ganglia of the invertebrata are able to discharge. CHAPTER VIII. AUGUST. Mud coloured by worms--Their retreat at alarm--A country duck-pond--Contents of its scum--Cryptomonads--Their means of locomotion--A Triarthra (three-limbed Rotifer)--The Brachion or Pitcher Rotifer--Its striking form--Enormous gizzard--Ciliary motion inside this creature--Large eye and brain--Powerful tail--Its functions--Eggs. In the beginning of this month a pond in the Finchley Road, a little beyond the Highgate Archway, supplied some more specimens of the _Pterodina patina_, described in a previous chapter; but towards the middle of the month a visit to Chipstead, in Surrey, enabled a new region to be explored. It is always a treat to a Londoner to get down to any of the picturesque parts of Surrey; the trees exhibit a richness of foliage and variety of colour not seen within the regions of metropolitan smoke; the distance glows with the rich purples so much admired in the pictures of Linnel, and the sunsets light up earth and sky with the golden tints he is so well able to reproduce. Probably the warmth of the soil, and the purity of the air, may make Surrey ponds prolific in microscopic life; but of this we do not know enough to make a fair comparison, although our own dips into them were tolerably lucky.