239 



3. The Anterior Head-Cavities of Acanthias. 



(Preliminary notice.) 

 By Julia B. Piatt, Worcester, Mass. 



eingeg. 22. März 1890. 



Acanthias embryos have a pair of head-cavities anterior to the 

 »premandibular cavities« of Balfour. 



These cavities are somewhat wedge-shaped. The point of each ex- 

 tends forward and outward below the optic vesicle, while the base lies 

 anterior to the base of the mandibular cavity, and dorsal to the lateral 

 prolongations of the so-called »first« head-cavity, i. e. that cavity which 

 meets the corresponding cavity of the opposite side below the point 

 of the notochord. 



Van Wijhe^ has figured a pair of 

 cavities which he found in Galeus, ante- 

 rior to the premandibular. He had how- 

 ever, but two specimens of Galeus, both at 

 the beginning of stage K, and finding that 

 in these embryos the walls of the anterior 

 cavities were somewhat thinner where they 

 came in contact with the walls of the pre- 

 mandibular cavity, he supposes the ante- 

 rior cavities to be cut off from the preman- 

 dibular, adding, »die Abschnür ung hat 

 wohl noch nicht lange stattgefunden«. 



In AcantJiias the anterior head-cavity, 

 is from the first independent. It arises, 

 shortly after the formation of the preman- 

 dibular, as a split in the anterior meso- 

 derm. 



The accompanying camera outline from a horizontal section 

 through the base of the anterior cavities, through the lateral prolonga- 

 tions of the premandibular cavity, and through the body of the man- 

 dibular, shows their relations to one another in the plane of the section. 



However, as the mandibular cavity extends upward, it at the same 

 time extends forward, so that its anterior part lies just above the base 

 of the anterior cavity. 



Thus the wall of the anterior cavity comes in contact with the 

 walls of both the premandibular and the mandibular cavities, but its 

 lumen is not continuous with that of either cavity. 



In the angle towards which the three cavities converge lies the 

 ciliary ganglion. 



1 Über die Mesodermsegmente und die Entwicklung der Nerven des Selachier- 

 kopfes. Amsterdam, 1882. 



