EARLY DEVELOPMENT OF HYDRA. 1 7 



of the pseudo-cell (Fig. i6, a and b, PI. III.). Here one sees 

 a thin rim of darkly staining material which is usually more 

 prominent in one hemisphere though occasionally a continuous 

 one is found (Fig. i6, U). Within this rim are the nucleolar bodies 

 often forming a considerable mass or, as in the figure, spread out 

 singly with their edges closely applied to each other. The in- 

 terior of the structure takes a plasma stain but slightly and is 

 very homogeneous in character. Fig. i6, c, PI. III., is a draw- 

 ing of a pseudo-cell in which some of the nucleolar bodies were 

 in the pole opposite to that in which the darkly staining mass 

 was found. They are evidently of a different nature than the 

 others as the stain is apparently largely a plasma one. 



The cause for the changes above outlined may possibly be due, 

 as pn^viously noted, to a substance secreted by the cytoplasm of 

 the Q^^. This evidently causes a separation of the nuclear ele- 

 ments and they become arranged as above described. Further 

 study on the processes which take place in the absorption of these 

 bodies may serve to make clear the advantage, if any, which re- 

 sults from the arrangement of the material after the fashion above 

 described. Sometimes the pseudo-cell lies in a conspicuous 

 vacuole and at others none can be distinguished. The metamor- 

 phic changes are not entirely comparable to digestive processes 

 for they cease for a time with the peripheral disposition of the 

 darkly staining elements. The nuclein, which is highly resistant 

 to digestive ferments, may serve to protect the contents of the 

 structure from further changes. 



2. Pseudo-cells Derived from Nuclei. 

 There are a considerable number of pseudo-cells which are 

 derived from the nuclei of the nourishing cells. In such cases, 

 after being taken into or fusing with it, the cytoplasm seems to 

 blend with that of the egg and then changes occur in the 

 remaining nuclei which are similar to those described as taking 

 place in the nucleus of the whole cells which are transformed 

 into pseudo-cells. The nucleolar bodies do not cause the rup- 

 ture of the nuclear membrane, but there is an evident separation 

 of the nuclear elements, as the peripheral darkly staining rim 

 clearly shows (Fig. 17, PI. III.). This process is comparable 



