340 
MR. J. DALRYMPLE’S DESCRIPTION OF AN INFUSORY 
of the parent, and a few moments after is actively engaged in searching for its 
food. 
Such is the most common form of reproduction ; but towards the latter end of the 
season, the females are found with a totally different form of ovum within them, 
Plate XXXIV. fig. 9. This ovum is spherical and dark, the outer covering appearing 
to consist of an aggregation of cells whose rounded form may best be seen at the 
circumference, where they appear clear and semi-transparent. Beneath this external 
layer is a second stratum of cells containing pigmentary molecules, that obscure the 
view of the yelk within, although there may be faintly seen four or five larger cells, 
with so highly a refracting outline as to give them much the appearance at least of 
oil-globules, Plate XXXIV. fig. 6. As the ovum becomes a little further advanced the 
peripheral cells are expanded, slightly club-shaped and striated, giving the whole 
ovum the aspect of a dark spherical body regularly covered with fine strise (Plate 
XXXIV. fig. 7), radiating from a centre : from the want of general transparency no 
distinct germinal vesicle can be seen. 
1 have not had sufficient opportunities to trace the further development of these 
ova, but Mr. Brightwell of Norwich, an excellent and most accurate observer, has 
watched them for some months after their expulsion from the parent, without ob- 
serving any further change. These ova are however so totally distinct in their phy- 
siological relations to the production of the embryo from the germinal vesicle of the 
ovum lying naked in the ovisac, that I think it probable they are destined to remain 
through the winter undeveloped, until the following year, as it will be seen that the 
period of the summer, during which this animalcule is found, is unusually short, as 
compared with the date of existence of congenerous species. 
A third appearance (or description of ovum) is met with in the ovisac of the 
parent female. We observe an embryo developed gradually from a germinal vesicle, 
until it begins to assume a definite shape and independent movement, when we are 
at once struck with the great difference of its form, size and organization. This is 
the male, and as it is in itself most curious, and as I believe up to this time quite 
new and unique, it will require special Klescription. 
This male (Plate XXXIV. fig. 1 1) is about three-fifths the size of the female, generally 
resembling it in shape, but more flattened at the lower part or fundus, and more 
prolonged at the side corresponding to the vaginal opening in the female, and which 
in the male presents a similar valvular opening though comparatively smaller in ex- 
tent, Plate XXXIV. fig. 1 2 E. Within this valve is observed a short canal leading to a 
large spherical bag (Plate XXXIV. fig. 12 G), which may be distinctly seen filled with 
molecular bodies in constant tremulous movement. From this sac, which I shall 
denominate the sperm-bag, a short but thick rounded body (Plate XXXIV. fig. 12 F) 
projects into the canal before mentioned as leading to the lateral opening, and around 
the extremity of this projecting process, and even within it to a short distance, is a 
visible ciliary motion indicating a canal (Plate XXXIV. fig. 14 C) : on the neck of the 
