ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
457 
Before invagination the endoderm becomes differentiated into a primary 
or archenteric, and a secondary or vitelline layer. The prostomial 
mesoderm arises by a splitting of endoderm. Although at first outside, 
the sickle and the primitive plate subsequently grow into the shield. In 
the tortoise the endoderm is separated as a continuous layer from the 
yolk ; in the gecko the elements are separated singly, and afterwards 
form a layer. The arclienteron is hollow throughout its whole extent, 
and its extent is absolutely and relatively greater than in the gecko. 
Vertebral Column of Triton.* — Prof. C. Hasse demonstrates in 
Triton tseniatus the metamerism of the skeletogenous tissue, and the 
fundamental importance of the elastica externa in the formation of the 
vertebral column. The tailed Amphibians have not only an elastica 
externa or cuticula sheleti and an elastica interna or cuticula chordse , but 
between these a sheath, arising from the skeletogenous tissue and not 
from the chorda, which forms the intervertebral cartilage of other 
authors. 
Development of Connective Tissue in Siredon.f — Dr. F. Maurer 
distinguishes, according to their genesis, three groups of connective tissue 
- — dorsal, intermediary, and ventral. The dorsal connective tissue arises 
from the protovertebrse, and may be divided into median and lateral 
portions. The dorso-median connective tissue is laid down in the 
sclerotome-diverticulum (axial-connective tissue of Babl). The dorso- 
lateral connective tissue arises from the cutis-layer (dermal connective 
tissue of Babl). The intermediary connective tissue is separated off 
from that region where the somatopleure and the splanchnopleure of 
the lateral plates bend into one another, and is associated mesially with 
the dorso-median tissue. The ventral connective tissue arises from the 
parietal plates (visceral connective tissue of Babl), and may be divided 
into a median portion arising from the splanchnopleure, and a lateral 
portion arising from the somatopleure. The detailed results of Maurer’s 
investigation go to justify this classification. 
Embryology of the Sea-Bass.J — Dr. H. V. Wilson has studied the 
development of Serranus atrarius , the Sea-Bass. The pelagic ovum is 
about 1 mm. in diameter, the membrane is thin and horny, the yolk a 
translucent sphere, with a single large oil-globule uppermost in the 
floating egg. In the ripe unfertilized egg the yolk is covered by a thin 
layer of protoplasm. Shortly after fertilization this concentrates towards 
a point just opposite the oil-globule. A couple of hours after fertiliza- 
tion there is found at the lower pole of the floating egg a disc of proto- 
plasm lenticular in section, thinning away into a very delicate layer 
around the yolk. The yolk itself is without any protoplasm except near 
the oil-drop, which has a cap of coarse protoplasm. The patch or 
blastodisc at the lower pole is at first circular, but by the time the first 
two blastomeres are marked off the germ is bilateral or biradial. The 
segmentation, which is of the ordinary bilateral type characteristic of 
Teleostei, is described with great clearness. Careful observation suggests 
* Zeitschr. f. Wiss. Zool., liii. Suppl. (1892) pp. 1-20 (3 pis.). 
t Morphol. Jahrb., xviii. (1892) pp. 327-48 (1 pi.) 
i Bull. U.S. Fish Commission, ix. (1891) pp. 209-77 (12 figs., 20 pis.). See ante , 
p. 188. 
