ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 387 



a chromatin portion forming head and axial filament. This is uncovered 

 on the upper surface of the head, but enveloped further down, and in the 

 tail by an achromatin or parachromatin sheath. 



First Branchial Cleft of Chick.*— Mr. F. P. Mall finds that on the 

 fourth day of incubation four small tubercles are formed round the 

 ventral half of the first branchial groove ; these, the colliculi branchiales 

 externi, mark the beginning of the external ear ; a little later a sack -like 

 process, the canalis tubo-tympanicus, grows from the lateral aboral part of 

 the branchial pocket, and forms the primitive drum-cavity. From the 

 aboral end of the second arch an embryonic operculum projects over the 

 third and fourth arches ; the operculum and the main part of the second 

 arch unite with their fellows of the opposite side to form a horseshoe 

 hoop around the ventral part of the neck. Before this is well formed, the 

 two colliculi branchiales extend of the second arch separate from the 

 rest of the arch, and aid in forming the external ear. The third and 

 fourth arches form a depression which is closed by the operculum blend- 

 ing with the thoracic wall. The tympanic membrane is formed by the 

 membrane of His. From the dorsal part of the cleft an involution of 

 ectoderm extends to the ganglion of the facial nerve and blends with it ; 

 this involution is one of the rudimentary branchial sense-organs, described 

 by Van Wijhe, Froriep, and Beard. 



Attachment of the Blastocyst to the Uterine Wall in the Bat.f — 

 Prof. E. van Beneden has studied in Vespertilio murinus the attachment 

 of the embryo to the mucous membrane of the uterus. He gives a brief 

 description of the uterus and of the successive relations of the ovum, but 

 devotes most attention to histological facts connected with the attachment 

 of the blastocyst. 



(1) The uterine epithelium degenerates completely. It disappears 

 over the entire cavity of the uterus. It cannot therefore have any share 

 in the formation of the maternal portion of the placenta. 



(2) In Vespertilio murinus, the uterine glands have no relation to the 

 placenta. They are wholly absent in that portion of the mucosa which 

 corresponds to the placental ring of the blastocyst. In the animal under 

 consideration there can be no question of the absorption by the placenta 

 of a glandular secretion, spoken of as uterine milk in other mammals. 



(3) At a very early stage in development, while the embryo is still 

 two-layered throughout, before the formation of the primitive line or 

 placental villosities, there obtains throughout the entire extent of the 

 placental ring so intimate a union between the embryonic epiblast and 

 the modified uterine mucosa, that it is difficult to distinguish the boundary 

 between maternal and embryonic tissues. 



Embryology of Anolis.J — Mr. H. Orr has investigated the embry- 

 ology of Anolis zagrsei. He finds that the notochord extends forward in 

 the head, along the line of the cranial flexure, and ends in a mass of 

 fused hypoblast or epiblast, which forms the dorsal part of the oral 

 fusion. From the hypoblastic portion of this mass of cells the head 

 cavities arise ; they retain for a considerable time their median con- 

 nection with the anterior end of the notochord. The relation of the 

 anterior end of the notochord, the head-cavities, and epiblast, precludes 



* Johns-Hopkins Univ. Circulars, vii. (1888) p. 38. 



t Bull. Acad. K. Sci. Belg., xv. (1888) pp. 17-2G, 1 pi. (not appended). 



X Johns-Hopkins Univ. Circulars, vii. (1888) p. 38. 



2 e 2 



