270 CONOCHILUS VOLVOX, 



the brown flocculent matter (which by the way is full of interesting 

 microscopic organisms) with which the water plants are at the present 

 time coated. 



There cannot be the least doubt that, these " sticks " are 

 Diatoms, though Mr. Hy. Davis, (by whom an interesting article 

 on C. volvox was wi-itteu and published in the " Monthly Microscopical 

 Journal " for July, 1876,) once entertained, I understand, the opinion that 

 they are Desmids, possibly belonging to the genus Docidium. This can 

 scarcely be so, as the bodies divide longitudinally, as do Diatoms, and 

 not transversely, after the manner of Docidium and other alhed Desmids. 

 They do not (at any rate the form commonly found) belong to the genus 

 Navicula, as Lord Osborne originally supposed, as they lack the charac- 

 teristic " median longitudinal line and nodules ;" and liis lordship's 

 observation that only one form is found in each colony, and that the size 

 of all the sticks in each is the same, the size varying with the dimen- 

 sions of the colony, does not accord vdth my own. In one instance I 

 found a decided Pinnulaiia, if not P. viridula a form excessively 

 like it — one specimen only aznongst a number of the common 

 kind. The Diatoms, either owing to the jelly of the Rotifers 

 not being a favourable medium for displaying the markings, or to the 

 fact that the latter are worn away in some mysterious manner, are most 

 difficult to resolve. Those which are free in the water are by no means 

 easy, and though "high powers" have been brought to bear upon them, 

 it is by no means clear which they are. I believe them to belong to 

 the genus Synedra, closely allied to, if not identical with, S. fasciculata. 



It is just possible that the plane spot at the centre of the valves may 

 have been mistaken for the line of transverse division. At first sight 

 it appears inexplicable that other bodies than acicular-shaped Diatoms 

 are rarely, if ever, found in these erratic jeUy-masses ; but when 

 we take into consideration that the jelly expands as the funnel- 

 shaped creatures emerge, and becomes compressed when they are 

 retracted, it is obvious the quasi tubes in which the animals 

 live are always " too tight a fit " to allow freedom of entry 

 for comers of every class, and it is simply owing to " Natural 

 Selection," (if it is lawful to adopt the expression,) and the 

 needle-pointed shape and hard and unyielding substance of the intruders, 

 that they ai-e able to gain a footing at the threshold. The sudden 

 retreat of the irritated hostess draws, perhaps, one of them in a little 

 way, the closely-pressing jelly retains it while its hostess cautiously 

 passes outwards. Another sudden jerk draws the unwelcome visitor 

 farther in, then another jerk and another, till the unbidden and perhaps 

 unwiUing guest reaches the middle of the globe and finds himself merely 

 one " stick " in a " rook's nest." 



The " Productive Pond," as Mr. Bolton styled it, now its stock 

 of C. volvox is exhausted, has a rich store of the exquisite Polyzoa, 

 PluinatcUn rcpem, growing unattached, twining in and out among 

 the rootlets of Lcmna minor. This condition is more favourable for 

 observation than when the polypidom adheres to a large plant such 

 as Potamogeton natans, upon which I usually find it hereabouts, as it is 

 readily seen with transmitted light and without obstruction. — S. S. R. 



