EuphaiisiicUe. 17 



in prepared eggs, (see PI. 1, figs. 4 — 6). It is also not 

 difficult to distinguish in the centre of each segment a 

 somewhat more opaque area, generally of a somewhat oval 

 or elliptical form. These central areas have also been ob- 

 served by Messrs. Brook and Hoyle, and are by them re- 

 garded as the nuclei of the cells. In suitably prepared and 

 stained eggs (see PI. 2) it is however easily seen, that in 

 reality they do not represent the true nuclei, but more pro- 

 perly the so-called centrosomes or attracting centres, by the 

 aid of which the chromatic substance of the nucleus is 

 divided into 2 perfectly equal parts, each of its con- 

 stituent corpuscles, the so-called chromosomes, being dimidi- 

 ated longitudinally. The true nuclei are very difficult to 

 observe in the earlier stages of cleavage, and it is only in 

 the more advanced stages of the gastrula that they appear 

 as distinctly defined vesicles. As above stated, oosphères are 

 occasionally found, in which the ovum is still unsegmented 

 (see PL 1, figs. 1,2), and must therefore be assumed to have been 

 just fecundated. When an ovum of this kind is suitably pre- 

 pared and stained, it shows the nuclear area on one of its sides, 

 invariably that side which in the fresh egg is turned 

 downwards. On turning the egg so as to get an end-view 

 (PI. 2, fig. 1), we find in the middle a dense assemblage 

 of flexuous fibres radiating from a central point and gradu- 

 ally evanishing towards the periphery, whereby a rather 

 large, but indistinctly defined, rounded area is formed of a 

 much deeper colour than the rest of the egg. This area 

 undoubtedly represents the primary centrosome, inside which 

 the nucleus is probably located ; but it has not been possible 

 for me to see the latter distinctly. The first cleavage of 

 the ovum, as usual, is preceded by a division of the 

 controsome, whereby 2 radiating areas are produced. These 



