POND LIFE : ANURIA LONGISPINA. 167 



Diatoms are mostly present in the pretty stellate species, Asterionella 

 formosa, with a few specimens of Synedra and Pleurosigma, while 

 desmids are fairly plentiful in the beautiful forms of Pediastrum 

 granulatum and Hyalotheca ; Pandorina morum, Clathrocystis, and other 

 algse have also been found. 



It may not be out of place to remark that a recent visit to Olton 

 reservoir yielded most of the good finds of last year, not omitting 

 Lcptodora hyalina and Hyalodaphnia Kahlbergensis, the former translucent 

 beauty being scarce, but the latter abundant, with other rare entomostraca, 

 and that at the " Koll Call " the only missing friends were Anurcea 

 longispina and Ceratium longicorne, a gap well filled up from an unex- 

 pected source. 



Possibly some who take great interest in the purity of the water 

 supply of Birmingham may feel alarmed by this somewhat formidable 

 list of "dreadful sounding" names of the living organisms it contains, but 

 perhaps it may help to comfort them to suggest that the presence of these 

 organisms should rather be taken as indicative of the general good 

 quality of the water than otherwise, as some of them, at least, are at 

 home and abroad known as the inhabitants of deep, clean water only. 



BRITISH LICHENS : HINTS HOW TO STUDY THEM. 



BY W. PHILLIPS, F.L.S. 



(Continued from page 128.) 



If a thin, perpendicular section be taken of one of the foliaceous 

 species, say for example Physcia parietina, and placed under the micro- 

 Bcope with a little water, there will be presented to the eye of the student 

 three distinct layers. (Plate V., Fig. 9.) 



1st. — The cortical* layer, which forms the upper surface or bark of 

 the thallus. It is composed of minute cells, closely compacted together, 

 constituting a firm membranaceous tissue. (Plate V., Fig. 9a.) The cells vary 

 in size and outline, the latter being modified by their mutual pressure. 

 The cell walls are comparatively thick, and by transmitted light show a 

 faint degree of colour, more conspicuous in very old specimens of the 

 Lichen. Beneath this cortical layer will be seen — 



2nd. — The gonidial\ layer, which consists of cells filled with 

 chlorophyll, spherical, or nearly spherical, varying in size, and easily 

 separated from each other by the slightest pressure. There would 

 appear to be no actual union between these bodies, though produced one 

 from the other, but they lie loosely together in a tolerably well defined 

 stratum. (Plate V., Fig. 9b.) They occur in the thallus of all Lichens, 

 though they differ considerably in form, being first, cells enclosing green 



* From cortex, Latin for rind or bark. 



\ From yovri, generation, and ddos, resemblance, indicating their resemblance 

 in function to the spores. 



