68 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Cell-Lineage of Planorbis.* * * § — Mr. S. J. Holmes gives a preliminary 
account of his researches on this subject. Gastrulation is embolic, the 
blastopore being elongated and slit-like. It closes from behind forwards, 
and the mouth appears later at the final point of closure. For details 
as to the origin of the cells, reference must be made to the original. 
Worm-like Spermatozoa of Paludina vivipara.j — Dr. E. von 
Erlanger describes these remarkable spermatozoa (Carnoy, 1884 ; Auer- 
bach, 1896). There is a refractive axial filament of alveolar structure, 
a likewise alveolar and transversely striated protoplasmic sheath, and a 
terminal tuft of twelve cilia. The author suggests a comparison with 
the structure of a muscle-fibre. 
Young of Cryptochiton4 — Mr. H. Heath describes the external 
features of Cryptochiton stelberi , one of the most modified types of Poly- 
placophora. In the adult, no trace of the tegmentum is visible, the 
articulamentum alone remains. In the young, there is a series of eight 
openings along the median dorsal line, corresponding to the posterior 
portion of each valve. They are about 0 • 5 mm. in diameter, and through 
them the shell is plainly visible. On carefully dissecting out the valves, 
a well-defined tegmentum is visible. The type is not primitive, but re- 
presents the last of a series which has undergone successive modification, 
by which the tegmentum, originally the same size as the articulamentum, 
has gradually disappeared. Palaeontological evidence also supports 
this conclusion. 
5. Lamellibranchiata. 
Experiments on Bivalves.§ — Dr. J. B. Pieri has experimented with 
species of Tapes , Venus, Artemis , and other bivalves. They do not be- 
come habituated to a diminution of salinity by 1/2 or 1/3, nor to an in- 
crease of 2 per cent., nor to an increase of iodide or bromide of potassium ; 
in short, they have little power of adaptive reaction to changes in the 
medium. Vapours of creosote make the heart-beats slower, and end in 
their stoppage; laudanum applied to the heart, or injected, stops the 
beats at once, but they may re-commence in. 15-25 minutes ; vapours of 
laudanum are but slightly injurious ; pure nicotine in contact with the 
heart stops it at once ; a weak solution makes the beats slower ; cocaine 
acts as a very powerful muscular poison, having an effect even when 
diluted to 1/000 ; cyanide of mercury is still more injurious; even when 
diluted to 1/30,000 it has an effect. 
Head-kidney of Lamellibranchs.|| — Dr. H. Stauffacher has investi- 
gated the structure, function, and development of the head-kidney in the 
trochosphere of Cyclas cornea. In opposition to Ziegler, he finds that 
it is an unpaired organ, and actively functional. It consists of an in- 
ternal ciliated portion opening into the primary schizocoele, of a middle 
portion formed of two complex cells, and of an external portion consisting 
of a vesicle opening to the exterior by a fine canal and pore. The lumen 
is wholly intracellular. In development, the inner and middle regions 
* Zool. Bulletin, i. (1897) pp. 95-101 (3 figs.), 
t Anat. Anzeig., xiv. (1897) pp. 164-7 (1 fig.). 
x Proc. Acad. Nat. Sci. Philadelphia, 1897, pp. 299-302 (1 pi.). 
§ Arch. Zool. Exper., v. (1897) pp. 251-79. 
H Zeit. wiss. Zool., lxiii. (1897) pp. 43-61 (1 pi. and 4 figs.). 
