ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
355 
A Two-headed Tadpole.* * * § — Mile. M. Loyez describes a tadpole of 
Itana temjporaria hatched with two heads. These were at first equal 
and symmetrical, and each bore on its outer side the usual external 
gills. When the external gills were replaced by the internal set, only 
one spiracle was formed — to the left side. Very soon the left head 
began to gain the preponderance. There were four adhesive organs, 
but the tadpole was never seen to fix itself. It swam well enough, and 
lived for three weeks. It ate by its left mouth only, at least after the 
inequality began to be apparent. Its size at death was less than that of 
the others of the same brood. 
Blood-formation in the Lamprey.j — Dr. E. Giglio-Tos finds that 
the hsematopoetic organ of the larval lamprey is the so-called spiral valve 
of the intestinal wall. The parenchyma of this fold includes three kinds 
of cells : — (a) the mother-cells, which give rise to (b) hacmocytogenous 
cells, from which are derived (c) the elements of the blood, the erytliro- 
blasts and the leucoblasts. Thus the red and white cells have in this 
case a common origin. Mitosis is the mode of division of all the 
elements as long as they are included in the stroma of the valve ; the 
erythroblasts do not contain haemoglobin in their early stages when they 
are within the stroma of the valve ; the pigment begins to be produced 
when they reach the plasma of the blood. 
Development of Dental Enamel.J — Dr. R. R. Andrews gives an 
account of his researches on the development of dental enamel and a 
criticism of the results reached by Dr. J. L. Williams.§ In the con- 
clusion of his paper he expresses his belief that the formation of the 
enamel is in a sense a secreting process, though he does not believe that 
secreting papillae have been found in the stratum intermedium in all 
cases. This requires further investigation. There are two distinct 
products of the enamel-forming layers. One of these products, from 
which the enamel-rods themselves are built, is formed in the amelo- 
blasts, but not by nuclear formation. In the formed enamel-rod the 
globular bodies are nearly or quite melted into one another at their 
extremities. 
As the globular bodies pass from the ameloblasts, they are placed in 
a network of what appear to be epithelial fibres, which pass within, 
between, and across the globular masses. Around the scaffolding thus 
formed the protoplasmic exudate flows, thus supplying the cement sub- 
stance. Calcification then takes place, and enamel is formed. 
Mesoderm of the Anterior Region of the Head in the Duck.|| — 
Prof. H. Rex has made a contribution to this difficult subject. It is not 
easy to make a summary intelligible without the author’s figures, but the 
main — though tentative — result is as follows. The Anlagen of the paired 
pre-mandibular head-cavities (and the canal connecting them) are formed 
as lateral outgrowths from the degenerate and solidified apical part of 
the anterior region of the gut. The hollowing out of these rudiments 
* Bull. Soc. Zool. France, xxii. (1897) pp. 146-8 (4 figs.). 
f Atti E. Acc. Torino, xxxii. (1897) pp. 362-76 (1 pi.). 
X Internal. Dental Journal, April 1897, 20 pp., 12 figs. 
§ Cf. this Journal, ante, p. 261. 
l| Arch. f. Mikr. Anat., 1. (1897) pp. 71-110 (Fpl. and 12 figs.). 
