2 PROF. M. M. HAllTOG ON THE 



have been most valuable and suggestive. Zenker's paper, the first serious attempt to 

 grapple with the internal structure of this group, is full of gross errors of fact and inter- 

 pretation ; and Vernet, the last student of the genus, having dissected but little, has 

 added little to our knowledge. 



I Avish gratefully to acknowledge much friendly advice from Professors A. Milnes 

 Marshall and G. S. Brady ; valuable help in preparing sections from Mr. Walter Langton, 

 Laboratory Assistant at Owens College; and some excellent drawings made by my 

 friend Mr. J. Macpherson, student in Queen's College, Cork. 



For the species my choice has fallen on C. brevicornis, Claus (Das Genus Cijcl. &c. 

 p. 32, t. iii. figs. 12-17), which I believe to include as a not very distinct variety the 

 later species C. (jigas, CI. (Weitere Mittheil. p. 207, figs. 1-5) ; to this it is referred by 

 my friend Prof. G. S. Brady, P.B.S., and my descriptions of the proportions of the 

 appendages &c. refer to this solely. 



The habitat of Cyclops is fresh and brackish water, usually in pools and back- 

 waters. The species under consideration is fairly abundant, and occurs with other 

 species, notably C serrulatus, C. coronatns, and C. temiicomis, in gatherings made in the 

 neighbourhood of London, Birmingham, Manchester, and Cork (where it occurs in both 

 fresh and brackish water). It is tolerant of captivity, breeding freely in pickle-bottles, &c.j 

 but usually in time degenerating in size, though often gaining in transparency. It feeds 

 usually on living animals (e.rj. Rotifers, the youngest of its own species, &c.), but will 

 eat dead aquatic animals, and, in the absence of other food, browses on algse, of which 

 its stomach is sometimes full. 



To obtain specimens in quantities for stocking-purposes, sweeping with a large muslin 

 net may be resorted to ; for taking specimens from the jar I use a dipping-tube, much 

 narrowed above to jii'event recoil, and bevelled below to make entrance more certain ; 

 "with this it is easy to catch animals resting against the glass of their receptacle, towards 

 which the bevelled side of the tube is held. The proportion of males to females is very 

 variable : every gathering has some of each. Males are more abundant in autumn and 

 winter. 



Methods. 



Examination of the living specimen is of course for many things absolutely necessary. 

 In confinement under the cover undue pressure is avoided by putting under a frond or 

 two of duckweed [Lenina). This arrangement has the advantage that by a push at the 

 edge of the cover the Cyclops can be rolled over and over to show in turn back, side, or 

 belly. In this case the legs are usually bent forward, seldom the reverse; but the 

 position may be arranged, before covering, with a needle under the simple microscope, 

 the Cyclops usually shamming dead when touched. 



Careful management of light and selection of objective are all-important. Points 

 clearly made out imder a wide illuminating ray and a low-angle objective disappear 

 under other conditions, and vice versa. I have found the Abbe condensor invaluable 

 for this work. 



For dissection I use French spear-head needles, and w^ork chiefly with a Chevalier's 



