306 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
grouping the chief emphasis is laid on the number of thoracic segments, 
the bristles, and the operculum. 
Neck-Glands of Leech.* — Dr. S. Apathy describes tfce salivary 
glands, or, as he calls them, the neck-glands, of the medicinal leech. 
He notes their exact position in the 7th, 8th, and 9th segments, and 
gives full instructions as to the mode of procedure in collecting the 
secretion of the glands, which prevents the coagulation of blood. The 
secretion is constant, and leeches collected at any time of the year, of 
any age, and without regard to the state of nutrition, maybe used. But 
animals of middle size, in which the clitellum is not swollen, will yield 
the best results. 
For a fuller treatment of the subject, and for details as to structure 
and function of the glands, Dr. Apathy refers to his recently published 
paper on “ The neck-glands of Hirudo medicinalis, with regard to the 
clinical use of their secretion.” t 
Rotatoria. 
Researches on the Plankton of Ponds.f — Dr. 0. Zacharias has ex- 
amined a large amount of plankton material collected by him and for 
him in po :ds in various parts of Germany, in order to compare the micro- 
fauna and flora swimming or floating in the open water with that found 
in larger freshwater lakes. He gives a list of about 100 species of 
organisms found therein, 36 being Rotifers. Two of these are described 
as new : — Brachionus falcaius and Tetramastix opoliensis , both of which 
are described and figured. 
Determination of Sex in Hydatina Senta.§— Prof. M. Nussbaum 
has followed Maupas in experimenting with this Rotifer in regard to 
the determination of sex. He begins by describing the animal ; but it is 
not necessary for us to do more than re-state the essential facts as to 
the reproduction. The male is much smaller than the female (up to 
0*25 mm. in length), without alimentary canal, and very short-lived 
(2-3 days). In copulation, which occurs especially with young females, 
the penis perforates the skin, and the sperms are discharged into the 
body-cavity. Fertilisation of the eggs does not necessarily follow 
insemination. The adult female measures 0*75 mm. in length ; it may 
attain full size two days after hatching. The eggs are cither “ summer 
eggs ” with soft shells, or “ winter eggs ” with hard shells ; the “ sum- 
mer eggs ” give rise to a male or a female brood, and are produced 
especially by females which have not been inseminated ; the “ winter 
eggs ” are produced only by females which have been inseminated. Nuss- 
baum has convinced himself that the “ summer eggs ” are never fertilised, 
and that the “ winter eggs ” always are. Any one individual produces only 
one kind of egg. But Nussbaum shows in this connection that the dimen- 
sions of the eggs are not quite reliable proofs of the sex of the forth- 
coming brood. On the whole it is true that the larger eggs develop into 
females, and the smaller into males, but the size varies considerably, 
and the medium-sized eggs are difficult to deal with. Thus, while Plato 
* Biol. Centralb]., xviii. No. 6 (1898) pp. 218-29 (2 figs.), 
t SB. Med. Nat. Siebenburg. Mus. Verein, xix. (1897). 
x Forseliungsber. a. d. Biol. Stat. zu Plon, vi. (1893) pp. l-£0 (1 pi ). 
§ Arch. Mikr. Anat., xlix. (1897) pp. 227-308. 
