ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
19 
one another by limiting areas or diastemas.” Their primary origin 
is from incomplete processes of division ; but they may also arise 
secondarily by the marginal coalescence of previously distinct cells. 
Both types occur abundantly in the blastoderm of fishes. The author 
maintains that syncytia, pluripolar nuclear division, and giant-nuclei 
or syncaryoses, are associated phenomena implying intense plasmie 
activity and favourable nutritive conditions. The paper is beautifully 
illustrated. 
Effect of Gases on Development.* — Herr P. Samassa finds that 
hydrogen has a much more deleterious influence on frogs’ ova than 
nitrogen has. In pure oxygen the development was normal for the first 
four days; in the absence of oxygen it also proceeded normally for 
some time. The ova of Ascaris megalocephala can survive being kept 
for months without oxygen, but in hydrogen or nitrogen they died. Pure 
oxygen greatly inhibited development of the Mscans-eggs ; at a pressure 
of 2J atmospheres of pure oxygen, development stopped, and the eggs 
were all dead on or before the eleventh day. 
Spiral Fibre of Mammalian Spermatozoon.t — Herr C. Benda now 
agrees with A. von Brunn that the spiral thread round the connecting 
or middle piece of the spermatozoon is formed by the apposition of 
protoplasmic granules. These are not, however, ordinary components 
of the plasm, but new, and probably of some specific function. 
Theory of Biogenesis.^ — In the second volume of his work on the 
cell and the tissues, Prof. O. Hertwig expounds afresh his theory of 
development. There are two sets of factors : — (a) external or environ- 
mental, including the interactions of the cells amongst themselves ; 
(6) internal or inherent in the hereditary idioplasm. There are two 
substances which together make up the living substance : — (1) the idio- 
plasm, which conserves the hereditary characters of the species, though it 
is at the same time modifiable by external influences ; and (2) a formed 
plasm or Protoplasma-product, which is moulded by the idioplasm. 
Inclining to a Lamarckian position, the author holds that the idioplasm is 
modifiable from without, and that lines of development and evolution are 
thus in part determined from without. 
Derivatives of the Visceral Clefts in the Lizard.§ — Herr F. Maurer 
notes that in Vertebrates with j)ermanently open clefts, the derivatives 
are the thyroid, the thymus (from the dorsal pouches of clefts 2-4), and 
the post-branchial bodies behind the last cleft. When pulmonary respi- 
ration begins, there are additional derivatives of the clefts, namely, the 
epithelial corpuscles and the carotid glands of Urodela, and besides 
these, in Anura, various residues of the internal gills. He proceeds to 
inquire into the state of affairs in Lacerta agilis. 
The primordium of the thyroid is formed as in fishes and amphibians. 
The post-branchial bodies appear, sometimes on the left only, sometimes 
on both sides, close behind the last cleft. The thymus primordia are 
* Yerh. Nat. Med. Yer. Heidelberg, vi. (1898) pp. 1-16. 
f Yerh. Anat. Ges. xii. Vers., in Anat. Anzeig., xiv. (1898) Erg.-kft., pp. 264-6. 
X ‘ Die Zelle u. die Gewebe. Zweites Buch. Allgemeine Anatomie und Physio- 
logic der Gewebe,’ Jena, 1898. 
§ Yerh. Anat. Ges. xii. Vers., in Anat. Anzeig., xiv. (189S) Erg.-hft., pp. 256-61. 
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