636 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
material at night gives a vivid idea of the activity and voracity of this 
group of worms. The classification of zones adopted by the author is 
regarded as purely tentative, and we still require much information as 
to the vertical distribution of Turbellaria. 
Mechanism of Stinging Cells in Turbellaria.* * * § — M. E. Penard 
has studied this subject in the Turbellarian Stenostomum. After point- 
ing out the insufficiency of current explanations of the mechanism 
by which the thread is discharged, he gives an account of his own 
observations and inferences. The stinging cells are ovoid, surrounded 
by a firm membrane, which at the anterior pole thins suddenly, so as to 
form a delicate pellicle closing the cell. The cell contains a nucleus 
imbedded in protoplasm, and also an inner capsule attached to the 
anterior end of the cell, and containing the spirally coiled thread. Also 
within the capsule are three processes radiating from the closing mem- 
brane, and surrounding the coil thread. When discharge is about to 
take place, the plasma of the cell becomes turgescent, and so exerts 
pressure on the internal capsule. The three rigid processes form a 
pyramidal cage around the thread, and so keep it in position until the 
pressure becomes too great for the closing membrane. This yields, the 
apposed points of the processes divaricate suddenly and widely, while 
their other ends remain attached to the evaginated capsule. By this 
means the thread is launched forth explosively, and is at the same time 
uncoiled through all its length. 
Eew European Land Planarian.j — Under the name of Bhyncho- 
demus pyrenaicus Prof. L. Graff gives an account of a new species of 
Land Planarian taken near St. Jean de Luz. The single specimen 
measured 53 mm., so that it was of considerable size. The integument is 
of a honey-yellow colour, except on the ventral side ; this last has a 
reddish-violet median part with the sides yellowish-grey. The species 
is declared by Dr. Simroth, who has described two Land Planarians from 
Portugal, to be unknown to him. 
Swedish Tricladidse.J — Herr D. Bergendal describes Gunda Ulvse , 
Uteriporus vulgaris, Dendrocoelum lacteum , Z). punctatum, Planaria torva , 
Pl. lugubris, PL polychroa, and the genus Polycelis. He has some notes 
on classification, and recognizes two families — Uteriporid® and Plana- 
riidse, the latter with Planari®, Polycelid®, and Gundid® as sub- 
families. 
Structure of Trematodes.§— Herr E. Walter has studied Monostomum 
trigonoceplialum Rud., M. reticulare van Ben., M. proteus Brandes, para- 
sites of Chelone viridis. After describing these species separately, he 
discusses some moot points in regard to the minute structure of 
Trematodes. To three of these we shall briefly refer. First, in regard 
to the parenchyma, Herr Walter distinguishes four types : — 
(1) In the most primitive state the parenchyma consists of a homo- 
geneous or finely granular substance in which nuclei are imbedded 
without distinct cell-boundaries, e. g. Distomum reticulatum. 
* Arch. Sci. Phys. et Nat., xxix. (1893) pp. 487-94 (5 figs.), 
f Bull. Soc. Zool. France, xviii. (1893) pp. 122 and 3. 
j Ofversigt K. Vetensk.-Akad. Forhandl., xlix. (1892) pp. 539-57. 
§ Zeitschr. f. wiss. Zool., lvi. (1893) pp. 189-235 (3 pis., 1 fig.). 
