
1891.] Embryology. ; A 1029 
Jurrow is visible while the first furrow has not finished.4 With the pass- 
ing of the furrows through the egg the nuclei pass to the middle. If 
they have reached this after the end of the second cleavage, then the 
segmentation proceeds more rapidly and regularly. 
A blastula stage follows, and from it the endoderm is formed at all 
points over the surface, by both delamination (Theilung) and migra- 
tion (Einwanderung). Later the blastula cavity is filled with solid 
endoderm. From the ectoderm the outer chitinous case is secreted, 
and later the inner germ-membrane. The ectoderm remains intact, 
and ‘goes over into that of the adult. The sequefice of the appearance 
of the tentacles does not follow any defined law. The mouth-pole is 
in all probability identical with the pole that gave rise to the polar 
bodies. 
Morphology of the Vertebrate Head.’—In the Anatomischer 
Anzeiger (VI. Jahr., ’91) Julia B. Platt publishes a contribution of 
the ‘‘ work presented last October for publication in the Journal of 
Morphology.’ The present paper deals with the origin of the head 
segments and their nerve supply. ‘‘ The anterior limit of the fusion of 
the edges of the neural plate is therefore not the neuropore, but the 
anlage of the optic stalk.. . . Theoptic nerve which later develops 
into the optic stalk is therefore primarily a dorsal structure, and mor- 
Phologically the first or most anterior of the cranial nerves. An- 
terior to the first gill-cleft, Acanthias has therefore seven pairs of- 
somites,—three for the hyoid arch, two for the mandibular, one pre- 
mandibular, and one ‘ anterior.’ ” 
In the Teleost Batrachus the author says: ‘* My study of the develop- 
ment of the mouth in Batrachus but confirms the work published 
many years ago by Dohrn on the development and significance of 
the teleostean mouth. At an early stage a pair of pockets from the 
alimentary canal open to the exterior anterior to the hyomandibular 
clefts. Much later in the development of the embryo the mouth 
breaks through in the ventral region of these pockets as a bilateral 
involution of the ectoderm, fusing with the endoderm, and opening to 
each side of a central partition sometimes before the median line is 
* The italics above are "y own. The relation between the cleavage of the protoplasm 



and the division of th a parallel case to that observed by Mayer in Pagurus 
and by E, B. Wilson in Renilla, wad ute most suggestive facts as to the relation cog 
between nucleus and cell- body, and e OY P A 
take place independently a the nucleus, yet show that th leus d ot dominate all 
cytogenic phenom H. M. 
5 Anatomischer PEE VI. Jahr., Nos. 9 and 10, 1891. 





