268 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
of Perameles, and to reassert Leche’s doctrine of tlie existence of pre- 
lacteal teeth. Besides these prelacteal teeth, there are traces of a fourth 
dentition capable of replacing the permanent teeth. As to the origin of 
the molars, the author supports Kiikenthal’s vie\y that they are the result 
of the fusion of the rudiments of the first dentition with the material 
out of which the second dentition would originate. He believes that the 
possibility of such fusion is proved by the facts observed by himself as 
to the fusion of Pd 3 and a prelacteal germ. In the case of the molars, 
the fusion is believed to be determined by the reduction of the jaw, which 
prevents the molars of the first dentition from developing until late, so 
that the hypothetical two sets of molars would develop at the same time 
did fusion not take place. 
Structure and Development of the Lens.* * * § — Prof. Carl Rabl pub* 
lishes the second of his memoirs on this subject, which deals in a very 
detailed way with the lens in reptiles and birds. A report must be 
deferred until the author sums up. 
Development of Gymnophiona.j' — Prof. A. Brauer continues his 
account of the development of Hypogeophis rostratus , one of the Cas- 
cilians, dealing in this instalment with the gradual assumption of the 
body-form. The contrast with Ichthyophis is interesting. 
While Ichthyophis has aquatic larvae, the young of Hypogeophis pass 
from the egg to a mode of life like that of the adults. Thus the de- 
velopment of Hypogeophis is relatively condensed, and the visceral 
apparatus, the segments, the limbs, &c., appear relatively early. The 
tail-fringe seen in Ichthyophis is quite absent ; the branchial aperture 
closes immediately after the degeneration of the gills, while it persists 
in the free larvae of Ichthyophis ; the integumentary sense-organs appear 
early, and disappear before hatching. 
Development of Thymus and Allied Structures.^ — Prof. F. Maurer 
divides the derivatives of the gill-clefts into two groups : — (1) those 
which may occur along with an open and functional gill-cleft apparatus 
(thyroid, post-branchial bodies, and thymus) : and (2) those which occur 
only after the obliteration of branchial respiration, and represent 
vestiges of a gill-cleft apparatus (epithelial corpuscles and carotid 
gland). In Lacerta agilis , the organs of the first group (with the 
exception of certain parts of the thymus) occur exactly as in fishes and 
amphibians. The thymus is restricted to the first three clefts; the 
first disappears, the second is quite homologous with that in An- 
amnia, the third extends further ventralwards than in Anamnia, and 
suggests its position in mammals. There are rudiments of two pairs 
of epithelial bodies, the anterior pair (in connection with the third cleft) 
represents the carotid gland in the lizard ; the posterior pair (in con- 
nection with the fourth cleft) undergoes early degeneration. The author 
gives some interesting comparative figures. 
Formation of the Corpus luteum.§ — Herr J. Sobotta has a short 
paper on Clark’s || recent work on this subject. He is of opinion that 
* Zeitschr. wiss. Zool., lxv. (1898) pp. 257-367 (6 pis. and 72 figs.), 
t Zool. Jahrb. (Abth. Anat.), xii. (1899) pp. 477-508 (4 pis.), 
j Morph. Jahrb., xxvii. (1891)) pp. 119-72 (3 pis. and 4 figs.). 
§ Arch. Mikr. Anat., liii. (1899) pp. 546-58. 
[| Arch. Anat. Phys. (Anat. Abth.), 1898. 
