370 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
and by the fusion of certain groups of their radii. Here the author’s 
results entirely agree with Driiner’s. 
Secondly, MacFarland describes the behaviour of the centrosomes in 
the maturation of the eggs of another Opistliobranch, Diaulula sandie- 
gensis (Cooper) Bergh. The second directive spindle with its centro- 
somes (but not including the mantle-fibres) arises by gradual growth 
and associated change of form from the inner centrosome of the first 
directive spindle. The daughter centrosomes arise from the division of 
the mother centrosome, but a residue is left which forms the central 
spindle. In short, as Heidenhain has said, “ central spindle and centro- 
somes are in their origin one whole.” The same is probably true in the 
case of the first polar body, but the difficulties of observation prohibit a 
certain conclusion. 
Structure of Apera Burnupi.* — Mr. W. E. Collinge describes the 
alimentary canal, pedal gland, and reproductive organs of this Natal 
slug. That Apera has affinities with the Testacellidee admits of little 
doubt, but there is a wide gap between it and either Testacella or 
Daudebardia. In the generalised character of its reproductive organs, it 
resembles in some ways the genus Schizoglossa, but here again there is a 
wide gap. 
5. Lamellibranchiata. 
Hinge-Teeth in Lamellibranchs.} — M. Felix Bernard discusses the 
morphology of the hinge-teeth. The Mytilidre furnish a starting pointy 
they and the other Anisomyaria illustrate the state which Neumayr 
called dysodont. From the normal dysodont type a regressive and a pro- 
gressive developmental series may be said to emerge. The former is 
illustrated by Plicatula and oysters ; the latter begins in Crenella and 
Aviculidao, becomes pronounced in Arcidae and Carditaceae, and is more 
and more accelerated in Lucinacete, Cyrenaceae, and other families, 
which show the division of the primitive plate into cardinal and lateral 
teeth. Considered mechanically, the evolutionary process is roughly 
this : — at first, the provinculum was enough to secure the fixity of the 
hinge ; dysodont teeth prevented dorso-ventral slipping ; the hinge grew,, 
the fine dentations became insufficient, the primitive plates curved and 
prevented both horizontal and vertical slipping ; division of labour 
occurred between the different segments, becoming always more precise 
in its effect, and precocious in its ontogenetic appearance. The total 
disappearance of the pro vinculum in the majority of Heterodonts is the 
natural consequence of this acceleration. 
Arthropoda. 
a. Insecta. 
Castes in Termites.} — A translation (by W. F. H. Blandford) is pub- 
lished of the second portion of the valuable memoir by Prof. B. Grassi, in 
collaboration with Dr. A. Sandias, on the constitution and development 
of Termite societies. The paper embodies the result of a long series of 
observations on Calotermes and Termes. From his study of these and 
* Arm. Nat. Hist., xx. (1897) pp. 221-5 (1 pi.). 
f Comptes Rendus, cxxv. (1897) pp. 48-51. 
% Quart. Journ. Micr. Sci., xl. (1897) pp. 1-75. 
