50 NATURAL SCIENCE [July 
The observations of Wesenberg-Lund (33) on the Rotifera of 
Denmark, lead him to adopt Nussbaum’s view that nutrition is the 
determining factor in the production of males. The chief result of 
his researches is to show that, immediately before the normal period 
of sexual reproduction, a period of very rapid parthenogenetic multipli- 
cation sets in, and it is when this has reached its height that males 
appear. Whenever it was seen that any one species was becoming 
predominant in the gatherings from one particular source, the ap- 
proach of the sexual period for that species could be predicted. He 
finds, however, that, with the same species of rotifer, the sexual 
period may occur at different times even in neighbouring ponds. 
Lauterborn, on the other hand, states that the appearance of males 
of the same species in very different localities, from lakes to puddles, 
was often striking in its simultaneity. 
Though only indirectly connected with the present subject, we 
may call attention in closing to some of the unexplained anomalies 
in the distribution of the Rotifera. While the great majority are 
notoriously sporadic and uncertain in their occurrence in any one 
locality, yet Lauterborn and others have recorded cases where the 
same species has appeared year after year in the same pool while 
absent from all the surrounding localities. Very many species seem 
to have a literally world-wide distribution, and their number is con- 
stantly being increased; yet there are instances of curiously re- 
stricted range, and this in cases where insufficient search cannot be 
adduced to explain their absence from certain areas. Thus Lacinuwlaria 
is common in many localities in England ; it swarms in every lough 
in certain districts in the west of Ireland, appearing in July, as Mr 
Hood (24) says, “as precisely to its season as the lapwing or the 
swallow,” and yet we are assured by the same excellent authority 
that it is entirely absent from Scotland. Until 1883 the same 
appeared to be the case with Stephanoceros; since then, Mr Hood tells 
us, he has traced the gradual extension of its range until it has 
become by no means rare in the lochs of Forfarshire and Perthshire. 
. W. T. CALMAN. 
University CoLtLece, DUNDEE. 
LITERATURE REFERRED TO 
. Ehrenberg, C. G.—‘‘ Die Infusionsthierchen, u.s.w.” Fol. Leipzig, 1838. 
. K6élliker, A.—‘‘ Furchungen und Saamenfiden bei einem Riderthiere.” Froriep’s 
Neue Notizen, xxviii., 16-20. October 1843. 
3. Brightwell, T.—*‘ Some account of a dioecious Rotifer allied to the genus Notommata 
of Ehrenberg.” Ann. Mag. Nat. Hist. (2) ii., 153-158, pl. vi. Sept. 1848. 
4. Dalrymple, J.—‘‘ Description of an Infusory animalcule allied to the genus Notom- 
mata of Ehrenberg, hitherto undescribed.”” Phil. Trans., exxxix. (1), pp. 381- 
348, pls. xxxill. and xxxiv. 1849. 
5. Huxley, T. H.—‘‘ Lacinularia socialis. A contribution to the Anatomy and 
Physiology of the Rotifera.” Zrans. Mier. Soc. London, (N.S.), i., 1-19, pls. 
1.-ili, 1858. 
6. Cohn, F.—‘‘ Ueber die Fortpflanzung der Riderthiere.” Zeztschr. Wiss. Zool., vii., 
431-486, pls. xxiii., xxiv. Dec. 31, 1855. 
Ne 
