ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
357 
Morphological Nature of the Hypochorda.* — Prof. H. Klaatsch has 
studied this enigmatical structure in embryos of Torpedo and Pristiurus, 
and, comparing these with AmpMoxus , comes to the conclusion that the 
hypochorda of Craniota is a rudiment of the epibranchial groove, which 
is functional in the lancelet. Both have an endodermic origin on the 
dorsal wall of the gut beneath the notochord and between the paired 
aortge. The occurrence of a hypoehordal groove in development is also 
noteworthy. 
In the adult lancelet the organ is restricted to the pharyngeal region; 
in young forms it extends further back. In higher forms the rudiment 
is extended far back over the gut ; but this is regarded as a secondary 
character. There is no warrant for deriving the hypochorda from meta- 
rneric dorsal diverticula of the gut. As to its degeneration from a 
functional groove to a mere band in part elastic, the modification of the 
respiratory pharynx may have something to do with it ; and it should 
also be noticed that its reduction makes the development of an unpaired 
aorta possible. 
Gastrula of Amphioxus.f — Prof. H. Klaatsch has studied this stage, 
especially in relation to the concrescence theory. The main result is 
that the blastopore of the lower Chordata is not closed by the concres- 
cence of lateral parts, that there is as little of a gastrula-raphe in 
AmpMoxus as in the higher Vertebrates. What occurs is a gradual 
narrowing of the blastopore, wherein the “ instreaming ” of cell-material 
plays its part, as Kopsch has shown for Amphibia. 
Skeletal Cartilage of Outer Ear in Monotremes.f — Prof. Gr. Ruge 
has made an interesting discovery in connection with this. The carti- 
laginous skeleton of the external ear in Echidna is closely associated 
with the hyoid arch. In Ornithorhynchus the condition is confirmatory, 
though more primitive. Thus the hyoid arch, before forming the rudi- 
ment of the stapes by the separation of a dorsal portion, manifests its 
formative activity in giving origin to the cartilaginous external ear in 
the Promammalia. 
Development of Gymnophiona.§ — Dr. A. Brauer has studied the 
■development of Rypogeophis rostratus and R. alternans from the Sey- 
chelles. The segmentation, unlike that of other amphibian types, is 
meroblastic. One side of the egg showed several layers of blasto- 
meres ; the other parts showed nuclei with cell boundaries visible peri- 
pherally ; these nuclei are derived from blastomeres which wander into 
the yolk. A segmentation cavity was represented merely by gaps 
between the deeper cells. 
In the next stage, in the laid eggs, some of the blastomeres form a 
superficial epithelial layer, while the others are scattered in the enlarged 
segmentation cavity. The former (the f ‘ animal ” cells) arrange them- 
selves more regularly, and assume a cylindrical form at the future pos- 
terior end of the embryo. At the posterior margin a broad transverse 
groove is formed, and there the animal cells are turned downwards and 
forwards. The lower “ animal layer ” thus formed grows forwards, and 
* Morph. Jalirb., xxv. (1897) pp. 156-169 (1 pi.). 
f Tom. cit., pp. 224-43 (1 pi. and 4 figs.). % Tom. cit., pp. 202-23 (6 figs.). 
§ Zool. Jahrb. (Abtli. Anat.), x. (1897) pp. 389-472 (4 pis. and 26 figs.) 
