42 



Appendices to Fourth Annual Report 



Lettering used in the Figures, 



A.P.= 



a. ex. -- 

 bl.-- 



b. r.-. 



c. p- 

 e.a.- 



ec.= 



671.= 



9-P-- 



g. p.^-. 



gp.^-- 



h. fy. 



:archiblast. 



= animal pole. 



^ anterior extremity. 



= blastopore. 



= thickened rim blastoderm. 



= cellular parablast. 



= embryonic axis. 



■■ ectoderm 



-- entoderm. 



= germinal disc. 



: germinal protoplasm. 



= ditto, collected at vegetative 

 (yolk) pole. 



= germinal processes pressed in 

 amongst the yolk, 



= lst horizontal (equatorial) fur- 

 row. 



= 2nd ditto 



k. = keel 

 ^.c.j9. = limit of cellular parablast. 

 me. = mesoderm. 

 P. — parablast. 

 p. ex. = posterior extremity. 

 p.h. = primitive hypoblast. 

 p.s. = perivitelline space (breathing 

 chamber). 

 pr. V. — proto vertebrae. 



s.c. = segmentation cavity. 

 V. P. = vegetative pole. 

 1;.^.=: viscous layer, 

 y = yolk imbedded in the germinal 

 area which is undergoing 

 assimilation. 

 y.g.=jo\k. granules. 

 y.s. = yolk spheres. 

 ;3.r. = zona radiata. 



Fig. 1. — Optical section of a living unfertilised egg. The mass of large yolk 

 spheres are best seen towards the centre, while nearer the periphery the small 

 ' yolk granules ' are represented by the smaller dots. In this stage the egg 

 envelope adheres closely to the vitellus. The germinal protoplasm is not 

 shown. 



Fig. 2. — Ovum 1 hour after fertilisation. There is a collection of germinal 

 protoplasm at the surface of the yolk ; the ' yolk-granules ' have disappeared 

 and the egg envelope has separated from the vitellus, between which is the 

 perivitelline space (breathing chamber). 



Fig. 3. — Ovum 4 hours after fertilisation, showing the commencement of 

 segmentation and the partial separation of the first two segmentation spheres. 



Fig. 4. — Optical section of the four cell stage (9 hours). Only two cells are 

 seen in section, and the first equatorial -(horizontal) furrow is shown at hp, 

 completing the bases of the first four segmentation spheres, and thus dividing 

 the archiblast from the parablast. 



Fig. 5. — Sixteen cell stage (11 hours), showing a portion of the protoplasm 

 constituting the parablast as having left the germinal area and sunk to the 

 yolk pole. 



Fig. 6. — Slightly oblique view of a sixteen celled stage (13 hours), in which 

 the commencement of a second horizontal furrow {hf.'^) is seen. 



Fig. 7. — Advanced segmentation stage (21 hours), showing a morula mass of 

 cells in the archiblast, at a stage shortly prior to the formation of cells in the 

 peripheral parablast. 



Fig. 8. — ^An ovum 25 hours after fertilisation, showing the first row of cells 

 in the peripheral parablast. 



Fig. 9. — Part of an ovum shortly prior to the extension of the disc over the 

 yolk (47 hours). 



Fig. 10. — An ovum early on the 3rd day, showing the formation of the 

 segmentation cavity and the germinal disc as it begins to extend over the 

 yolk. 



Fig. 11. — Stage a few hours later than that shown in fig. 10. The parablast 

 is not indicated in this figure. 



Fig. 12. — Still later stage (middle of the 3rd day), showing the mode in 

 which the extension progresses. 



Fig. 13. — Stage 3^ days after fertilisation, showing the cap like blastoderm 

 covering half the yolk. In the axis of the embryo the cells are several rows 

 deep. There is a thickened rim at the margin, but more towards the centre 

 the blastoderm is very thin. 



Fig. 14. — Optical section in the direction of the longitudinal axis of the 

 embryo (4j days), showing the anterial portion of the thickened rims, which is 

 pushed down over the yolk, and which later unites with the caudal extremity 

 of the embryo, thus closing the blastopore. The dotted lines represent the 

 thickened rim. 



