ZOOLOGY AND BOTANV, MICROSCOPY, ETC. 291 



cytoplasm of the epithelial cells, and it gives rise at its surface to a 

 cement similar to that produced by the terminal bars. The structure of 

 the zona pellucida is favourable for the conveyance of nutritive materials 

 from the maternal capillaries to the growing yolk. J. A. T. 



Eggs and Embryos of Bdellostoma. — J. D. F. Gilchrist {Quart. 

 Journ. Jlicr. Set., 1918, 63, 141-59, 2 pis.) describes the naturally 

 deposited eggs of the South African Myxinoid, BdeUostoma {Hcptatretus) 

 hexatrema, two of which contained well-advanced embryos. There are 

 numerous small projections on the surface of the shell, consisting of the 

 columns of the columnar layer modified at the apex. There are 

 numerous small fissures, probably respiratory apertures. The two polar 

 rings show the inner layer of the shell much enlarged, the outer much 

 reduced. The anchor filaments consist of all the layers of the shell, 

 the heads of the columns of the columnar layer being drawn out so as 

 to appear as striations. The anchors consist of the modified columnar 

 layer and the stratified layer. The segmental duct of the embryo occurs 

 at the distal end of the last tubule of the pronephros, but does not open 

 into it. It is found also at the distal end of the last tubule but one, 

 where, however, it becomes solid and disappears. The tubules of the 

 mesonephros are not strictly segmentally arranged, in that there are 

 six tubules in three segments of the body behind the pronephros, 

 though there is one tubule for each succeeding segment, as far as the 

 mesonephros extends. J. A. T. 



Development of Head-segments of Dogfish. — Edwin S. Goodrich 

 {Quart. Journ. Mkr. Sci., 1918, 63, 1-30, 2 pis., 1 fig.) has studied the 

 segmentation of the head in Scyllium canicula. There are three pro-otic 

 segments, corresponding to the profundus, trigeminal, and facial nerves. 

 Somite 1 is pre-oral ; somite 2 lies above the mouth, and is related to the 

 mandibular bar. Somites 3 to 8 lie above each of the six gill-slits, 

 and are related to the hyoid and five branchial bars. The three pro- 

 otic somites are supplied by the oculomotor, trochlear, and abducens. 

 The first meta-otic segment, with the glossopharyngeal root, contains 

 somite 4, which produces no myotome and has no ventral root. Three 

 more meta-otic somites, supplied by the occipital ventral roots, and 

 corresponding to the first three branchial branches of the vagus, 

 complete the cranial region. The eighth somite belongs to the first 

 spinal nerve, of which the dorsal root is absent or vestigial in later 

 stages, and to the fourth branch of the vagus. The author deals also 

 with the vagus and with the development of the chondrocranium. 



J. A. T. 



Earliest Movements of Dogfish Embryo. — P. Wintrebert {Bull. 

 Soc. Zool. France, 1918, 43, 42-4) describes in the embryo of Scyllium 

 canicula the early automatic movements of the myotomes. They are at 

 first independently unilateral, and they are independent of the nervous 

 system. The excised myotomic chain, after entire removal of the 

 nervous system, retains its power of automatic contraction. J. A. T. 



Morphogenesis of Duplicities. — E. I. Werber {Journ. Ejper. Zool., 

 1917, 24, 409-43, 27 figs.) has experimented with the eggs of the 



