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SUMMARY OF CURRENT RESEARCHES RELATING TO 
are altered. The spiral fibres are not simple, but are made up of very 
fine fibrils united by a resistant cementing substance. The spirals 
often present a granulated appearance, which seems due to the inswathing 
intermediate substance — in fact, to a likewise spirally d sposed sarco- 
plasm. The granular accretions may be termed “ sarcosomes ” in the 
sense in which Retzius used that term. On the whole, these spiral 
muscle-cells are closely analogous to the cross-striped type. Ballowitz 
also describes the network of axial sarcoplasm, in which numerous 
granules are imbedded. 
7 . Gastropoda. 
Asymmetry of Gastropoda.* — Prof. A. Lang attempts to explain 
the asymmetry of Gastropoda in a manner which can hardly be made 
intelligible without a reproduction of his explanatory diagrams. He 
regards the explanation of Biitschli as incomplete, and considers that it 
is the development of a high turriform shell which is the prime cause 
of the conversion of a crawling Gastropod into an asymmetrical animal. 
Boring Organ of Natica.f — Herr P. Schiemenz asks, and seems to 
have succeeded in answering an old question, “ How does Natica bore 
holes in mussel-shells ? ” By many arguments he shows that the round 
holes cannot be made by the radula. On the under surface of the pro- 
boscis, however, there is a complex circular gland, with an enormously 
developed glandular layer, and with one system of muscles so disposed 
that they certainly do not form a sucker, but in all likelihood simply 
compress the gland. As Natica bores its victims under cover of sand 
and cannot be directly observed, it is not certain that this gland is the 
boring organ, but it has an acid secretion (perhaps sulphuric) and in 
shape and size it corresponds with the holes. 
Nudibranchiata holohepatica porostomata.J— Prof. R. Bergh gives 
an account of this group of Nudibranchs, which includes two families — 
Doriopsidae and Phyllidiidfe — superficially very unlike, but structurally 
congruent. The former includes two genera — Doriopsis (60 sp.) and 
Doriopsilla (2 sp.), the latter four genera — Phyllidia (5 sp.), Phyllidiella 
(4 sp.), Fryeria (1 sp.), and PJtyllidiopsis (3 sp.). Of all the genera 
diagnoses are given. 
Nervous System of Heteropoda.§ — M. P. Pelseneer has made a 
study of the nervous systems of various forms of Heteropoda, and finds 
that the pleural ganglia are fused with the cerebral, and that in all the 
visceral commissure is crossed. He gives some details, and points out 
that they agree with those exhibited by such streptoneural Gastropods 
as are nearest to the Heteropoda ; this leads him to the conclusion that 
the Heteropoda are simply Prosobranchs whose external appearance has 
been modified by a pelagic life. 
Embryology of Chiton. |] — Mr. M. M. Metcalf has some preliminary 
notes on the development of the Chiton. Fertilization is effected in 
* Vierteljahrschrift Naturf. Gesell. in Zurich, xxxvi. (1891) pp. 339-71 (22 figs.). 
t MT. Zool. Stat. Neapel, x. (1891) pp. 153-09 (1 pi.). 
J Vert). Zool.-Bot. Ges. Wien, xlii. (1892) pp. 1-10. 
§ Comptes Itendus, cxiv. (1892) pp. 775-7. 
|| John Hopkins Univ. Circ., xi. (1892) pp. 79-80. 
