Royal Microscopical Society. 
47 
elite ; and it was not till 1848 that Mr. Brightwell of Norwich 
discovered a Rotifer with separate sexes in the genus Asplanchna. 
In 1850 Mr. Gosse announced his discovery of the male of another 
species of the same genus, Asplanchna priodonta, and in 1854 Dr. 
Leydig discovered that of a third, Asplanchna Sieboldii. Two years 
later Mr. Gosse published a paper in the £ Philosophical Transactions ’ 
“ On the Dioecious Character of the Rotifera,” and in it he described 
and figured the males of several species of Brachionus, of Poly- 
artlira platyptera, Sync] act a tremula , and Sacculus viridis ; besides 
stating that he had discovered certain unusually shaped ova (which 
were possibly male ova) in Melicerta ringens. There were also 
strong grounds for believing that the males of Hydatina senta and 
Notommata Brachionus, had been seen and described as new species 
of female Rotifers. 
So the case stood in 1856 ; and I am not aware of any further 
addition having been made to our knowledge except my own dis- 
covery of the male of Pedalion mirum. 
Now on looking at the list of species given above in which the 
males have been observed it strikes one at once that, with the single 
exception of Melicerta, they all belong to one group ; namely, to that 
of the free-swimming Rotifers : moreover, as it is probable from Mr. 
Gosses description that the ova he found in Melicerta were winter 
eggs and not male ones, the thought at once occurs that it is possible 
that the Rotifers may be divided into two great groups, the one 
dioecious, the other monoecious — the first including all the free- 
swimmers both loricated and il-loricated, and the second the tube- 
making Floscules and Melicertans, and the creeping Philodines. 
Indeed Professor Huxley, in his paper on Lcicinularia socialis, 
made this probability a very strong argument for considering the 
Rotifers as permanent forms of Echinoderm larvae — as in these larvae 
a similar difference in sexual character accompanies a difference of 
structure, very like that which separates the free-swimming Rotifers 
from most of the others. 
The argument was one that was hard to answer, for it rested on 
the supposed monoecious character of some of the largest and most 
common Rotifers, of creatures that are constantly being watched 
and studied in consequence of their great size and beauty. Indeed 
it does seem strange that no one should have seen during the last 
eighteen years the males of Stephanoceros or of the Floscules, if 
these creatures have any ; for the adult animals are fixed to the 
plants on which they are found, are of comparatively large size, 
and, what is still more to the purpose, have tolerably transparent 
tubes in which their eggs are deposited and hatched. 
Melicerta presents a difficulty in the opacity of its tube, and 
Conochilus in its roving habits ; but Lacinularia is free from each 
drawback, and yet hitherto its male has escaped observation. 
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