MATQRATION OF OVUM IN ECHINUS ESCULENTUS. 183 



tions stained either with " fuclisiu S " or " Bordeaux red.'' 

 There is frequently a second smaller deeply staining circular 

 body in the nucleus, but it has no regularity in position and 

 is not invariably present. I cannot in any of my prepara- 

 tions see the double nature of the threads described by 

 Haecker. Close to the nucleus, very frequently on the side 

 of that body towards which the nucleolus lies, there is some- 

 times at this stage a body which presents much the appear- 

 ance of the centrosome of a resting cell. It consists of 

 either a single granule or pair of granules, sometimes a 

 group of smaller granules enclosed in a circular area. While 

 this may represent a centrosome it is impossible to dis- 

 tinguish it from similar bodies with central granules that 

 may be found in other parts of the cell, which are un- 

 doubtedly cell inclusions, and therefore no structure can with 

 certainty be identified as a centrosome. 



vStructure of the Protoplasm. — Wilson (1899) has 

 shown that in the young ovum the protoplasm is granular, 

 and that as the ovum grows in size an alveolar structure is 

 assumed. In the youngest ova of my fixed material the 

 protoplasm presents a granular appearance which is certainly 

 not alveolar, and can hardly be termed reticular (fig. 1). lu 

 the fully grown egg the appearances vary according to the 

 stain. In fig. 3 the cytoplasm is represented as showing a 

 reticulum which is composed of separate minute granules ; 

 the meshes of this reticulum bound alveolar spaces. These 

 alveoli are on the whole rounded, and in this particular 

 specimeu, from which the iron hasmatoxyliu was very 

 thoroughly washed out and [replaced by a slight counter- 

 stain by fuchsiu; they were faintly red with a slightly darker 

 periphery. In fig. 2, on the other hand, the appearances are 

 different. The iron hteniatoxylin has not been so com- 

 pletely washed out, and the alveoli have retained the dark 

 stain, showing up as rounded dark points separated by an 

 unstained reticulum. Sometimes the centre of the alveolus 

 is occupied by a black dot, as if the centre had not been de- 

 colourised. Thus my preparations fully bear out WiLson's 



