104 



Part III — Twenty-seventh Annual Report 



into the tin at 8*2° C. For the temperature of the water from this time to 

 March 25 see Table, p. 106. 



The eggs on the three plates were examined at this date. Under the lens 

 the eggs of all three lots were seen to have been fertilized ; the blastodisc 

 and a wide perivitelline space were apparent. The double egg-membrane 

 was more or less distinctly made out. The egg of Lot III. measured 

 1*4 mm. across the outer envelope, while the yolk sphere was *9 mm. in 

 diameter. The eggs were stuck very fast to the glass plate, and could not 

 be dislodged by a brush. A knife was required to remove them. Of five 

 eggs examined, one was dead ; the others were in excellent condition. The 

 dead egg had a wide perivitelline space, but the yolk sphere was shrunken. 

 It appeared to have been fertilized. 



February 22 — An egg of Lot I. showed a large thick blastodisc now 

 saucer-shaped (fig. 2). The disc covers the yolk like a cap. A number of 

 rod-like crystals are present inside the zona, In Lot II. the saucer-shaped 

 disc had a comparatively thin outline (fig. 3). The blastodisc was composed 

 of very small cells ; it covered half the yolk sphere. The long crystals were 

 present on the inside and outside of the zona, and on the yolk sphere. 

 The two-layered structure of the zona was well seen, since the outer 

 layer (o) which adhered to the glass had broken off, exposing the inner 

 layer (i). The eggs of Lot III. were in the same stage as Lot II. 

 While the egg of Lot I. was in the Laboratory, viz., 4 hours, it 

 developed from the stage drawn (fig 2) to that shown by the egg of 

 Lot II. (fig. 3). 



February 23. — An egg of one of the lots which was examined on 

 February 22 was left till the following day in a glass cell, in which it was 

 barely covered with water. It had reached the condition shown in Fig. 4. 

 The blastoderm almost, if not quite, covers the yolk. 



February 25. — In Lot I, the embryo was about half-way round the 

 yolk (fig. 5). Kupffer's vesicle was not made out. The eye was dimly 

 visible. There were many long crystals on the outside of the zona ; they 

 were apparently larger than those noted before. 



On the plate of Lot II. the live eggs were at the same stage as Lot I. 

 (fig. 6). Long crystals were seen inside the zona. Kupffer's vesicle was 

 not seen. The blastopore seems to be closed. In the specimen drawn the 

 eye was not made out, but in another specimen it was distinct (fig. 15). The 

 head is shown in optical section in Fig. 16. A number of dead eggs on this 

 plate had not swollen out to the size of the live eggs. A slight perivitelline 

 space was visible, but it was not so extensive as that of a live egg. The dead 

 eggs were easily dislodged by the touch of a pipette, whereas the live eggs 

 stuck hard, and were forced off with a distinct jar. These dead eggs did not 

 appear to have been fertilized. 



Lot III. were at the same stage as Lot I. The crystals both inside and 

 outside the zona were very long and numerous. 



March 2. — A sample of the eggs of Lot I. was scraped off. All were alive 

 save one. The embryo now showed a free tail (fig. 7). At this stage the 

 embryo almost completely encircled the yolk. The eggs of Lot II. (fig. 8) 

 were slightly further developed. The tail was now further away from the 

 head. With the growth in length in the free portion of the tail, the snout 

 and the point on the yolk sac where the tail began have grown further and 

 further apart. Lot III. (fig. 9) was ahead of Lot II. The eggs of Lots I. 

 and II. were very dirty. 



March 4. — The eggs were doing well. The tail in Lot I. (fig. 10) has 

 grown much in length, although it is not much in advance of the stage that 

 had been reached by Lot III. two days previously. The embryo on Lot II. 

 was slightly further developed than Lot I. There was a large quantity of 

 crystals inside the eggs. Although Lot III. was fertilized one day later than 



