436 
MR. R. GURNEY ON THE CRUSTACEAX PLANKTON 
The seasonal cycle o£ the species cannot be determined with certainty 
from Dr. Pearsall's collections, which were mostly taken on the surface, and 
therefore are unreliable in the case of a deep-^vater species ; but a careful 
comparison of the records from the different lakes leads to the conclusion 
that there is only one period of breeding, namely in the autumn, and that 
the adults die after breeding, the species passing the winter either in the 
form of resting-eggs or as nauplii. In all the lakes mature specimens were 
rare or absent in spring and early summer, but were abundant in collections 
made between August and November. Females bearing eggs were found in 
Hawes Water in August, but in the other lakes only in September or 
October. If this is a true statement of the breeding cycle, it resembles very 
closely the cycle in L. macrurus—ixno\}\%v cold-water northern form. On the 
Table 8. — Measurements of Cyclops ahyssorur, 
Length 
(including 
furca). 
Furca. 
Per cent, 
of body. 
Fiircal Setae. 
Seta 3. 
Per cent, 
of body. 
Outer- 
most. 

3 
4 
Wastwater 
Crummock 
Coniston 
UUswater 
Hawes Water .... 
Windermere 
Grasmere 
1'35 mm. 
1-43 
1-44 
1-42 
1-45 
1-77 
1-68 
133 
13-8 
13-7 
11-6 
12-8 
118 
149 
100 
418 
402 
394 
388 
329 
346 
341 
481 
484 
485 
456 
379 
423 
424 
194 
186 
190 
190 
250 
169 
190 
■ 34'4 
35-3 
36'3 
33 
31 
31 
32-5 
other hand, SchefEelt (1908) and Burckhardt (1900) found two breeding, 
periods in the Cyclops of the strenuus-gvo\\\i studied by them in the Black 
Forest and Swiss Lakes respectively. It is not, however, clear with what 
race or species these authors were dealing, since the species of this group 
recognized by Sars and Lilljeborg as distinct have not been generally 
admitted, and many writers have followed Schmeil in including all within 
the species C. streimus. It seems certain that the three species C. lacustris, 
C. scutifer, and C. vicinus should be maintained. Whether C. abyssorum is 
sufficiently distinct from C. sirenuus as defined by Sars is rather more 
uncertain, but the evidence goes to show that it is a limnetic and cold-water 
representative of C. strenuus, which it is convenient to distinguish. It is 
readily distinguished from typical C. stremms by the greater length of the 
afitennse, of the furcal rami, and of the furcal setae. The much greater 
