OUTLTNKS OF THE DEVELOPMENT OF THE TUATAEA. 13 



The yolkj lying within tlie blastoderm, is of the usual yellow 

 colour. In the earlier stages of development (c) it appears to 

 be pretty uniformly soft and liquid, except where it is adherent 

 to the under surface of the blastoderm. It is full of large 

 transparent spheres and small granular spheres, floating freely. 

 The small granular spheres nearly all contain bodies which 

 may be termed '^ crystalloids " (fig. 107) ; otherwise they closely 

 resemble the yellow yolk-spheres of the hen's egg. The crys- 

 talloids are clear, transparent, rod-shaped or spindle-shaped 

 bodies with truncated ends. The sphere appears to be at first 

 simply granular, and about 0"029 mm. in diameter (fig. 107, a) ; 

 then the crystalloid appears within it (fig. 107, b), and gradually 

 increases in size, stretching the sphere as it grows, while the 

 granules of the latter gradually disappear xmtil finally the 

 crystalloid is left without any trace of the original sphere 

 (fig. 107, c). Occasionally two crystalloids appear in the same 

 sphere (fig. 107, cl) ; they may then give rise to irregular four- 

 sided bodies (fig. 107, e). I am inclined to think that ulti- 

 mately the crystalloids lose their form, and run together to con- 

 stitute the large transparent spheres which I regard as oil 

 globules. Already at Stage C the crystalloids in some parts 

 are aggregated apparently around the large transparent spheres, 

 this aggregation appearing to take place first just beneath the 

 blastoderm, where the yolk is already to some extent coherent. 



As development proceeds the absorbent blood-vessels dip into 

 the yolk from the yolk-sac, and the large transparent spheres, 

 each surrounded by a layer of crystalloids, become attached to 

 these vessels like onions on a string. This ropy or radially 

 columnar character of the yolk in the later stages of develop- 

 ment is very striking even to the naked eye (fig. 106). 



The closeness of the blastoderm to the shell, and the elastic 

 inward curling of the latter as soon as it is cut through, render 

 the successful removal of the embryo a matter of considerable 

 difficulty in the earlier stages of development. The embryo is 

 sometimes found adhering to the inner surface of the part of 

 the shell removed, and its remarkable transparency in the 

 earlier stages makes it still more difficult to manipulate. 



