166 THE ZOOLOGIST. 



the date mentioned, nor has it been seen since, either in the 

 pool at Chipperfield Common or in any other pool. 



The study of the periodical changes in the relative numbers 

 of forms of life which, like Synchceta pectinata, may always be 

 found in one and the same pool, and the study of the appearances 

 and disappearances of forms of life which, like Noteus quadri- 

 cornis, seem to appear only at certain seasons, offer an interesting 

 field of inquiry for naturalists who are able to devote sufficient 

 time to them. Even small pools, like those of Chipperfield 

 Common, Parsonage Farm, Langleybury, and Cholesbury Com- 

 mon, present, as my rough notes amply show, great and varied 

 changes of their inhabitants, both in species and numbers of 

 specimens. 



The remarks just made relate to the changes in the fauna of 

 one and the same pool- There is another field of inquiry which 

 seems to be at least a3 interesting. This relates to the 

 remarkable differences between the faunas of pools in the same 

 comparatively small area. These differences are most strikingly 

 shown when the rotiferan fauna of a pool like that of Chipperfield 

 Common is compared with that of Langleybury Pool, or with 

 that of the Berkhamsted Castle Moats. In these cases, however, 

 the conditions of life are quite different, there being but small 

 quantities of aquatic plants in Chipperfield Common Pool, while 

 Langleybury Pool and the Berkhamsted Castle Moats are nor- 

 mally very weedy ; there are also other important differences. 

 It is easy to understand why, in these cases, the rotiferan faunas 

 should be different in a marked degree. What are certainly more 

 perplexing, and perhaps more interesting, are the questions which 

 arise when a comparison is made between the rotiferan faunas 

 of pools in which the conditions of life seem to be more com- 

 parable. Take e. g. Langleybury and Parsonage Farm Pools, 

 and the moats of Berkhamsted Castle. All these are shallow, 

 their waters are usually quite clear, their beds are covered by 

 comparatively thick deposits of fine mud, and they contain large 

 quantities of aquatic plants; further, all three are old, and, as 

 far as I know, have not been disturbed for years. A comparison 

 of their rotiferan faunas, based on the preceding notes, shows 

 that several species, viz. Metopidia solidus, Pterodina patina, and 

 Salpina mucronata, are found in all three. These species are 



