602 SHEINA MARSHALL 



several interstitial cells, much larger than the rest, may be 

 seen undergoing nuclear changes. The chromatin has formed 

 a thick spireme thread, and in some cases the nuclear mem- 

 brane has disappeared. The nucleolus takes no part in this, 

 but lies unchanged in the midst of, or to one side of, the 

 spireme. This is in accordance with the observations of 

 Wager, who states that ' the egg begins its growth by the 

 coalescence of a group of the primitive ova ; this process 

 is frequently attended by a peculiar nuclear degeneration '. 



Later the egg appears as a hemispherical mass of protoplasm 

 with lobed edges, which lies with its base in contact with the 

 mesogloea. The protoplasm is reticular, and at this stage 

 contains none of the so-called ' pseudo-cells '. The nucleus 

 corresponds in size with the cell and contains a large nucleolus 

 and a number of smaller secondary nucleoli varying in size. 

 The egg grows by the absorption of other interstitial cells, 

 but at this stage the nuclei of the latter break down com- 

 pletely before absorption. The protoplasm of the egg is filled 

 with minute deeply staining dots, probably, at least in part, 

 the remains of the chromatin of the absorbed cells. 



At a later stage (Text-fig. 2, h) the egg protoplasm is filled 

 with a mass of degenerated cells (' pseudo-cells ') and inter- 

 stitial cell nuclei. Intermediate steps can be traced showing 

 the process of degeneration of an interstitial cell. The process 

 goes on both inside and outside the egg. In groups of inter- 

 stitial cells, usually at some distance from the egg itself, the 

 nucleus is seen in the centre of the cell, surrounded by a dense 

 mass of protoplasm. The nuclear membrane is hardly visible 

 or has disappeared entirely (Text-fig. 2, c, 1 and 2). This mass 

 moves to one side and applies itself to the cell- wall as a densely 

 staining mass (Text-fig. 2, c, 3 and 4). The nucleus is at first 

 visible as a darker body, but eventually the whole mass stains 

 so deeply that the constituent parts are indistinguishable 

 (Text-fig. 2, c, 5). Groups of these degenerate cells are found 

 in the ectoderm after the egg has separated and are possibly 

 used up by a subsequent egg. 



When the degenerative process takes place within the cyto- 



