SPECTACLE STAGE. 55 



imperfect embryos at this stage. Eggs which are absolutely tin- 

 impregnated show a well-defined annular ring when one-third of 

 the period of incubation has been accomplished. These eggs give 

 no trouble whatever, and are easily removed before packing for 

 transportation or laying down to hatch. It is a very different 

 matter with the imperfectly fertilised ova. In this case the blasto- 

 derm, on account of imperfect segmentation, does not differentiate 

 into well-marked embryonic layers. Blood is frequently formed 

 in lacunar spaces at the opposite pole to the embryo, and this 

 blood is very pale in colour. These are the eggs which occasion 

 the principal part of the daily work in the hatching-house. It is 

 true that an unimpregnated egg sometimes becomes opaque in the 

 hatching-trays, especially if the water be subject to changes of 

 temperature ; and if shaken in water, or even disturbed, a large 

 proportion of unimpregnated eggs will turn white ; but in a well- 

 managed hatchery nearly the whole of the unimpregnated eggs 

 remain clear throughout the season. I strongly suspect, when they 

 do turn white, the coagulation is caused by the penetration of 

 water through the micropyle. Where imperfect segmentation has 

 taken place, there is probably a passage of blastoderm between the 

 yolk and the shell, and the latter, being porous, probably supplies 

 more water than the puny embryo can absorb. The yolk will then 

 coagulate and the egg become opaque. The Mulberry Stage 

 affords an excellent test of impregnation in large pure-bred eggs, 

 but it will be easily seen that it cannot be relied on in the case of 

 eggs from young fish or with crossed fertilisation. The 



SPECTACLE STAGE, 



which is the second important stage, however, affords a test of 

 the character of experimental work. This stage is marked by 

 the appearance of a loop of globules anterior to the embryotic 

 line. This loop gradually enlarges, and passes backwards over 

 more than half the sphere, giving the egg at one time the ap- 

 pearance of a pair of spectacles, minus one eye, and a little later 

 bears a striking resemblance to the three legs on a Manx coin. 

 The left side of the eye of the spectacle stops in the position 



