162 l». .1. 800URFIELI) ON KMOMOSTKACA. 



necessity be done by co-operation, I hope this record will show 

 that, at least, a number of suggestive facts may be accumulated 

 by isolated workers. But it must be remembered by those who 

 may think of commencing or assisting in similar observations 

 apon this or other groups of pond-life, that, unless made with 

 care, such records are worse than useless, and this, of course, 

 implies that, if taken up at all, a considerable amount of 

 labour, almost bordering upon drudgery, must be expended 

 upon them. 



In the present case little has been attempted beyond the 

 mere noting of the species found at each visit. The record, 

 therefore, although quite reliable, I believe, as far as it goes, 

 does not throw much light on many points about which 

 information is sadly needed. In spite of this incompleteness, 

 however, there are a few results that appear to stand out 

 pretty clearly, and which, to some extent, justify the work. 

 The most obvious of these, if not the most interesting, is that a 

 rigidly local list has been formed. It is probably by no 

 means exhaustive, although the few additions made during the 

 last two years seem to show that it embraces by far the larger 

 number of the forms actually living in the Park. In common 

 with all other local lists, the present should have some value in 

 connection with the question of distribution, but it is impossible 

 to say anything on this point at present, owing to the very small 

 number of such lists hitherto published. Its relation to our total 

 known fresh-water Entomostracan fauna is, fortunately, more 

 definite, and a comparison with the latter may prove instructive 

 in several ways. Altogether, it appears that about 150 species 

 have been so fai* recognized as British, and they belong to the 

 various orders as follows : — Phyllopoda, 2 ; Cladocera, 63 ; 

 Branchiura, I ; Ostracoda, 51 ; Copepoda, 33. The number of 

 species here recorded for Wanstead Park is 60, namely: 

 Cladocera, 33 ; Branchiura, 1 ; Ostracoda, 12 ; and Copepoda, 

 14. The water-fleas of this little district are, consequently'-, 

 equal in variety to two-fifths of the fresh-water forms known 

 to inhabit the whole of the British Isles, while of the three 

 main orders, the Cladocera show a proportion of a little over a 

 half, the Copepoda somewhat under a half, and the Ostracoda 

 a little under a quarter of the full records in each order 

 respectively. The I'elative smallness of the Ostracod list may 



