304 



MISS E. A. FRASER ON THE DEVELOPMENT 



Description of Material. 



TricJiosurus vulpecula. Embryo of G.L. 5 mm. ( = Stage \.a, 

 h k cf. (Text^figs. 1, 2.) 



This stage is represented by tl)ree embryos, a (S '97), b (lA. '01), 

 and c (I. '01), of Avhich («) and (c) are cut horizontally and 

 (b) longitudinally. 



The cavity of the optic vesicle is flattened by the thickening 

 and partial invagination of its lateral wall, and it is connected 

 with the brain by a hollow stalk. The ectoderm opposite the 

 vesicle is thickened. 



Text-fitrure 1. 



a.c.a. 



Y-X^m 



Tricho.sums vulpecula, 'G ih. biam. {h'Q']). 



Hot-izontal section througli tlie head (S 3-4-o), somewhat oblique, passing tlirough 

 tlie pi-emaudibiUai' head-cavity of the left side. X 75 and reduced by J. 



«.c.rt.=arteria cerebri anterior, JF'J?.=fore-brain. G.F. = trigeminal ganglion. 

 Z./?.c. =left head-cavitj'. i{.=portion of cavitj' constricted otl' from the re&t. 

 q^.y.=optic vesicle. v,c.in.==\'eM& capitis luedialis. 



There are two large and conspicuous head-cavities, one on each 

 &ide immediately posterior to and on the medial side of the optic 

 vesicle, situated ventro-laterally to the fore-brain ; between the 

 cavity and the brain runs the anterior cei'ebral artery. The 

 cavity is lined by a single layer of epithelial cells which is more 

 attenuated on the side fai'thest from the brain, where it carniot 

 everywhere be distinguished in the sections. The shape of the 

 cavity varies slightly in the three embryos, 'being obliquely 



* Vide Frasei- and Hill: "The Development of the Thymus, Thyroid and 

 Epithelial Bodies in Trichox^rus vulpecida" Vh.\\. Trans, lioy, iSoc. 1915. 



