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POPULAR SCIENCE REVIEW. 
parent, highly refractive globules, separated by a space about 
equal to their own diameter. These are the eggs in their 
primary rudimentary stage. The nucleus may generally be 
discerned hi each as a dull spot, surrounded by a bright space. 
One of these eggs enlarges rapidly, and gradually becomes more 
and more granular, until it is almost wholly opaque. It is now 
become well defined, and assumes the size and yolk form 
proper to the mature egg; but this shape is not constant, for 
being as yet destitute of a shell, the soft and yielding yolk is 
forced into ever-changing forms by the varying pressure of the 
digestive and other viscera in their proper motions, and in those 
communicated to them by the inflexions and contractions and 
elongations of the body. 
Meanwhile, what is termed segmentation of the yolk takes 
place. The turbid, semi-opaque mass maybe seen to be divided 
across the middle into two masses, each of these into two 
more ; and so on, until the whole has become a mulberry -like 
mass of small cells. When this stage is reached, the dull 
opacity disappears, and is replaced by translucency, in which, 
however, we begin to discern a complex array of organs 
and viscera. The egg now contains a living embryo, whose 
movements within its enveloping integument as well as those 
of some of its organs, as for example, its jaws and its vibratile 
cilia, can be discerned with ever increasing distinctness. These 
motions are rendered more distinct, — are more readily deter- 
mined to be proper to the embryo, and not communicated from 
the viscera of the parent, — by the circumstance that the envelope 
has now hardened to a firm, elastic, perfectly transparent shell, 
accurately elliptical in outline, from the internal wall of which we 
see the embryo recede at various points, waywardly and irregu- 
larly. Besides the organs I have named, two crimson specks 
may be seen near one extremity, and an opaque, undefined mass 
at the other. Both of these are seen to more advantage by using 
the direct light of the sun reflected from the stage of the micro- 
scope with a dark background. Then the red specks come out 
perfectly defined and of the richest vermilion hue, in the midst 
of the evanescent viscera, and the opaque posterior spot is seen 
to be quite white. The former are the eyes, which I shall 
speak of presently; the nature of the latter is not certain. 
Dr. Leydig supposes it to be an urinary concretion. It is very 
frequently seen in newly-liatched young Rotifeea and in the 
males, I think, always (see plate iv. fig. a). 
Development op the Embryo. — Dr. Mantell was the first to 
observe the development of the young in Stephanoceros ; and 
in his “ Thoughts on Animalcules ” he has recorded some 
interesting results of his investigations. I have myself verified 
