ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 149 



tion of the layer of jolk entoderm surrounding? the jolk-mass of the 

 monotreme egg. The primitive streak is originally entirely independent 

 of the primitive knot and its " gastrulation-cavity "; there is a sub- 

 sequent intimate approximation of these structures. There is well- 

 marked neuromeric segmentation of the cephalic region of the flattened 

 medullary plate, a clear differentiation of early plate-like ganglionic ex- 

 pansions of the neural crest in the cephalic region, and various cellular 

 connections between the cephalic ganglionic plates and certain of the 

 neuromeric segments of the medullary plate. The " archencephalic " 

 subdivision of the cephalic portion of the medullary plate, from which 

 the fore brain and most, if not all, of the mid brain are derived, is 

 relatively insignificant. 



Embryonic History of Carotid Arteries in Chick.* — G. H. Twining 

 finds that the branches of the external carotid when first estal)lished. 

 are derived exclusively from the ventral carotid. This condition is 

 seen in embryos incubated for 4^ days ; it persists until the middle of 

 the fifth day, at which time a spur is developed from the dorsal vessel 

 which, gradually becoming larger, forms an anastomosis with the ventral 

 vessel, so that by the sixth day the blood supplying the upper and lower 

 jaw is derived from two sources. The dorsal branch grows larger, while 

 the ventral carotid atrophies in its middle portion. The development of 

 the carotid arteries in birds is very similar to the development in reptiles 

 (Crocodilia) ; there are also broad resemblances between the process of 

 formation in birds and mammals, with difference in detail. 



Origin of the Vertebrate Eye.f — G. Jelgersma argues in support 

 of the view that the simple endoneural eye of the Ascidian larva — -which 

 is conceivably derivable from an Invertebrate eye if we think of the 

 neural canal as primitively open — -may be taken as the starting point for 

 the evolution of the Vertebrate eye. It is true that the eye of the 

 Ascidian larva has a lens which develops from the tissue of the neural 

 wall, and it is an unpaired eye. But the author seeks to show that these 

 differences do not present serious difficulties in the way of the homology 

 suggested, and he is nothing if not ingenious in making a strong case 

 for his theory. 



Egg's of Reptiles. J — G. Hagmann describes the eggs and the 

 hatching of the eggs in the Brazilian Geckonid, Gonatodes humeraUs, 

 and in another lizard, Tiipinambis nif/ropunctatus. In both cases the 

 eggs are laid in termitaries. He also describes the Qgg of Caman 

 sclerops, and notes, as an interesting instance of " isolation," that while 

 G. sclerops and G. niger live together, their sexual periods are separated 

 by four months. 



Buccal Glands and Dental Strands in Anura.§ — R. Oeder finds 

 that the glandular follicles of the toad arise singly or in groups, in con- 

 nection with the choanse and with the palate. In the frog the glandular 



* Anat. Anzeig., xxix. (1906) pp. 650-63 (7 figs.). 



t Morphol. Jahrb., xxxv. (1906) pp. 377-94 (1 pi.). 



X Zool. Jahrb., xxiv. (1906) pp. 307-16 (3 pis.). 



§ Jen. Zeitsclu-. Natunv., xli. (1906) pp. 505-48 (2 pis. and 14 figs.). 



