5 
On the Male of Rhinops vittrea. By G. F. Rousselei. 
described the males of Braehionus pala, rubens , amphieeros, baker i , 
angular is, dorcas , and mulleri , Sacculus viridis, Polyarthra platy- 
ptera and S 'ynchseta tremula, which fully established the dioecious 
character of the Rotifera. Of late years a large number of other 
male rotifers have been discovered, and quite lately (in April last) our 
Journal reproduced two fine drawings of the male of Stephanoceros 
eichhorni , the discovery of which is due to Mr. John Hood ; the total 
number of species of which the males have been recorded is now 
about 64, a few of which, however, are doubtful. 
The chief characteristics of all male rotifers so far described 
are : their diminutive size, and the total absence of a mouth, mastax, 
jaws, oesophagus, gastric glands, stomach, and intestine, the ovary 
being replaced by a large sperm-sac. 
In the male of Rhinops vitrea (plate I. fig3. 1 and 2) which it is 
my privilege now to describe, the conditions are altogether at variance 
with what have so far been considered the essential characters of male 
rotifers, and quite a new type of male is here found to exist. 
At an excursion organised by the Quekett Microscopical Club to 
Esher on the 2nd of May last, we came upon a small pond which was 
found to contain Rhinops vitrea in considerable numbers, and as usual 
I filled a bottle of strained water from this pond. Upon examination of 
this water at home in a trough I observed a small elongated rotifer of 
somewhat different shape swimming swiftly among the more bulky 
and slower female R. vitrea ; it attracted my attention and I thought 
it might possibly be the as yet unknown male of this species, espe- 
cially as it played round the females according to the most approved 
fashion in Rotiferland, and a number of females had large spiny resting 
eggs, known to be the result of fertilisation, in their body-cavity. I 
therefore isolated a few specimens in a compressor for examination 
with a high power, and soon discovered that it was not only a male, 
but a male possessing fully developed jaws and functional digestive 
organs. The internal organs differed in no way from those of the 
female, except that the ovary on the ventral side was replaced by 
a rounded sperm-sac, in which the spermatozoa could be seen wriggling, 
prolonged into the usual copulatory organ. It was next necessary to 
demonstrate that this was really the male of Rhinops, so I isolated two 
stout females, the young in this species being always developed in the 
uterus within the body and brought forth alive, as in Asplanchna, and 
after a few hours I found several of the same males swimming about 
with the two females. I also isolated some other females so as to get 
some quite young females to compare as to size and shape with 
the males, and from these I found that the newly born females are 
considerably larger in bulk than the males, and that they resemble 
absolutely the adult females in shape, though somewhat smaller in 
size ; moreover, the ovary with bright germ-cells is seen very 
distinctly in the young female. 
As will be seen by the accompanying figures, for which I 
