210 WAGENER, ON GYRODACTYLUS ELEGANS. 



constrictions on its surface plainly indicate an incipient mul- 

 tiplication by division. 



When the number of cell nuclei which arise in every part 

 of the segment-spheres, as well at the periphery as in the 

 centre, has increased, they necessarily approach the surface, 

 on which they cause visible protrusions. This appears to be 

 the commencement of the exit of the cells from the segment- 

 spheres. The nucleus must derive something from its nidus 

 because bare nuclei with nucleoli are never seen attached in a 

 very irregular manner to the segment-sphere [vitelline mass], 

 but always cells. The opening through which these cells 

 escape, owing to the viscous condition of the ovum above 

 noticed, of course closes so as to be invisible. 



The embryonal-cells adhere to the ovum only by a very 

 small part of their periphery, although I have never seen 

 them to become wholly detached, however active the move- 

 ment of the animal might be. 



The cells do not at first, any more than the segment- 

 spheres, occupy the entire uterine cavity. Both float in a 

 very clear fluid. At a later period the cells increase in 

 number, whilst at the same time they diminish in size. 

 The remains of the segment-spheres [of the vitelline masses] 

 which are also reduced in size, retain the spherical form, until 

 finally the cells cover them completely. The fluid at the 

 same time disappears, and the uterus closely embraces its 

 contents. 



In this condition the embryo represents an egg-shaped 

 mass of cells, which, within certain limits, are variable in 

 dimensions, and have a very clear nucleus, an opaque, oval or 

 rounded nucleolus, and equally opaque contents. 



The remains of one or both of the segment-spheres, usually 

 of both, rarely of one only, remain still visible for a considerable 

 time. They are always found in the situation where the 

 uterus of the embryo is afterwards formed. They are both 

 still present, when, under a strong magnifying power, the 

 commencement of the large hooks and of the sixteen small 

 points around the caudal disc may be plainly seen at the lower 

 end of the cellular and as yet perfectly oval embryo. 



But this appears to be the limit to their future development. 

 About this period one only of them is visible, surrounded 

 with cells at its lower border, which may be distinguished 

 from those constituting the parenchyma of the embryo by 

 their being encompassed by a fine elliptical line. These cells 

 are of very various sizes, representing in miniature the 

 irregular process observed in the large segment-spheres. 

 At a later period the remains of the other segment-sphere 



