38 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
of the visceral arches, with which they have more to clo than with the 
nerves. It seems as if in higher Vertebrates the periaxial strand had a 
diminishing share in forming the nerve-bearing tissue. The nerve- 
bearing tissue of the facial in birds is wholly due to the periaxial 
strand, that of the glossopharyngeal is partially so, that of the vagus not 
at all. 
Development of Teeth in Iguana.* — Dr. W. Leche has made some 
observations on a large number of well-preserved embryos and young of 
Iguana tuberculata. In an embryo twenty-four days old he found the 
first rudiments of the teeth ; these differed from those that appeared 
later by their smaller size, their superficial position, and their want of 
function, as they disappear long before birth. The second dentition of 
Iguana , as of other Saurians, differs, first of all, from that of Mammals 
in that the rudiment of the tooth is much further developed before it is 
“ emancipated ” from the enamel ridge. 
Development of Gill-pouches and Aortic Arches in Chelonia.f — 
From a study of Chelonia viridis , Dr. J. F. van Bemmelen comes to the 
following conclusions : — 
(1) The first formation of gill-pouches and aortic arches in Chelo- 
nians agrees completely with that of Lacertilia and Ophidia, but their 
further development is more like that of Birds than of other Reptiles. 
(2) There are primitively five pouches and six arches, and, in 
addition, there is developed from the hinder wall of the hindermost pouch 
a pair of pocket-like evaginations, as in Snakes. 
(3) The three anterior pouches are without doubt open for a short 
time, and it is probable that the same is true of the fourth pouch. 
(4) The first, as in other Amniotes, gives rise to the Eustachian tube ; 
the outer opening soon closes. 
(5) The dorsal tip of the second pouch widens out into a follicular 
epithelial bud; as in Birds the second pouch aborts in the course of 
development. 
(6) The backward growth of the gill-arches causes the outer cleft- 
like opening of the most anterior pouch to be pushed far back, and a 
long thin canal results. 
(7) The third pouch enlarges into an epithelial follicle with a 
number of secondary outgrowths ; this becomes constricted off from the 
branchial enteron, and the enlargements are converted into thymus- 
tissue, in the interior of which the central epithelial follicle persists. 
(8) The fourth and fifth pouches give rise to processes which retain 
their epithelial character. 
(9) The aorta is developed from the fourth gill-arch artery, and the 
pulmonary artery from the sixth ; the fifth early becomes aborted. 
Maturation and Fertilization of Egg of Axolotl.| — Prof. R. Fick 
finds that the eggs of the Axolotl vary considerably in size. The “ clear 
directive spot ” is not identical with the “ directive pit ” or fovea germina- 
tiva, for the latter is a pit in the surface of the egg, secondarily formed 
by the pressure of the first polar globule. The egg has two yolk- 
membranes, the outer of which is thick and derived from the follicular 
* Anat. Anzeig., viii. (1893) pp. 793-800 (7 figs.). f Tom, cit., pp. 801-3. 
% Zeitschr. f. wiss. Zool., xlvi. (1893) pp. 529-614 (4 pis.). 
