568 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Embryonic Circulation in Stickleback." — R. Antliony has studied 

 the primary circulation in Gasterosteus gymnurus. The heart is 

 markedly to the left. The first vessels are the first branchial arches in 

 continuity with the ventricle. A complete circuit is soon formed — 

 heart, first branchial vascular arches, roots of the origin of the dorsal 

 aorta, the aorta, the sub-caudal vein, the anal vein, the sub-intestinal 

 vein, the vitelline vein, the heart. This state of affairs lasts for some 

 hours. 



The following complications occur : 1. There is formed a vascular 

 vitelline plexus, at first to the left, then bilateral. It is posteriorly 

 venous ; it becomes arterial further forward, being formed by ramifica- 

 tions of the mesenteric artery. 2. Anterior cardinal veins and posterior 

 cardinal veins develop. They form the ducts of Cuvier, ^t first 

 asymmetrical and to the left, the right one behind the left. 3. The 

 cephalic arteries develop. Symmetry is slowly established. 



Anthony points out that the primary asymmetry corresponds closely 

 with that persistent in Amphioxus. It is probable that asymmetry is 

 general in the development of the vascular system in Teleostei. Ryder 

 has noted the displacement of the heart to the right m Apeltes quadracus. 



Gastrulation in Selachians.f — P. Wintrebert has studied this 

 process in the dogfish {ScyUium canicula), observing the living ovum 

 and also making sections. The gastrula cavity is produced by a cytula- 

 tion of a vitelline syncytium ; it is situated between the latter and the 

 endodermic-vitelline cells which migrate to the deep surface of the 

 blastoderm. In the first stage the gastrula is peridiscoidal or peribl^tu- 

 dermic, largely open to the exterior. In the second stage it is embryonic, 

 localized in the posterior region which will form the embryo ; it then 

 takes the form of a vesicle with a narrow blastopore, in most cases a 

 fissure. Tiiese two stages are antecedent to what has been called the 

 gastrula, which is a semilunar sub-caudal extra-embryonic space whei'e 

 the gut will be formed later. The author indicates how the peridis- 

 coidal gastrula of Selachians is represented in other types. 



Atresia of (Esophagus in Loggerhead Turtle Embryo.| — H. E. 

 Jordan has studied the atresia of the oesophagus which begins in the 

 embryo of the Loggerhead Turtle {Garetta caretta) on the twelfth day, 

 and is a normal developmental condition. During the tenth and 

 eleventh days of incubation the epithelial hning of the oral end of the 

 oesophagus (oesophageo-respiratory primordium) thickens greatly dorsally 

 as a result of extensive cell-proliferation. Daring the twelfth day the 

 cylindrical tube of the oesophagus becomes compressed dorso-ventrally. 

 thus bringing the dorsal and ventral epithelial walls into close apposition. 

 The apposed central cells fuse and form a plug of tissue, essentially a 

 mesenchyme-like syncytium. By the sixteenth day the atresia has 

 extended into the orifice of the larynx. The chief factor in the 

 temporary closure of the oesophagus is the change in shape from an 



* Comptes Rendus, clxv. (1917) pp. 474-6 (2 figs.). 



t Comptes Rendus, clxv. (1917) pp. 411-3. 



$ Carnegie Inst. Washington, Publication No. 251 (1917) pp. 345-60 (4 pis.). 



