70 THE FORAMINIFERA 



In my first observations the water circulating in the tanks of the 

 laboratory was used ; and though I repeatedly saw the protoplasm 

 emerge from the parent shell and break up into spheres, the development 

 did not pursue a normal course. Again and again the spheres, after 

 remaining separate for some hours, fused with one another, and finally 

 the mass broke up into irregular globular bodies of very unequal size, 

 which remained alive for days, but did not, in most cases, secrete a shell. 

 It was not until fresh sea-water was used in the jars that I had the 

 pleasure of witnessing the normal process of development. 



In view of this experience, and of the fact that though I have ex- 

 amined some thousands of specimens of Polystomella, I have never met 

 with a megalospheric form with a central chamber less than 34 p in 

 diameter, I am inclined to think that the great irregularities in size in 

 the brood of young, and the small diameter of some of them, are the result 

 of abnormal development. 



In some genera, however, as stated below, the two forms cannot always 

 be distinguished by the size of the central chamber. 



Nuclear Changes. When, in the reproduction of the microspheric 

 form, the megalospheres first become isolated, the centre of each is 

 occupied by a sharply -defined, round nucleus, about 7-8 /* in 

 diameter, staining uniformly pink in picrocarmine. At this stage 

 there is also diffused in the protoplasm a material taking a stain 

 in this reagent; but in a short time the stained material, pre- 

 viously diffused, becomes aggregated in defined but irregular 

 masses, which gradually draw together, and for a time frequently 

 hide the nucleus from view. When two or three chambers of the 

 young test have been formed the nucleus is again distinctly visible 

 (Fig. 11, b, N), together with one or more irregular masses (n) 

 formed by the closer aggregation of the previously diffused 

 material. In many cases, though not in all, a mass apparently 

 identical with the latter remains visible in or near the central 

 chamber in specimens of the megalospheric form in advanced 

 stages of growth ; but it is, I believe, the round nucleus which 

 was seen in the megalosphere at its first formation which becomes 

 the nucleus (" principal kern ") of the megalospheric form. 



The relation between this nucleus and the nuclei and irregular 

 strands of the microspheric parent has not been followed. 1 



Growth and Reproduction of the Megalospheric Form. As the 

 individuals of this form grow, and the number of their chambers 

 is augmented, the nucleus likewise increases in size, and, leaving 

 the megalosphere, it moves on through the chambers, becoming 

 temporarily constricted as it passes through the narrow passages 

 connecting them. In specimens fairly advanced in growth the 



1 I have not met with any evidence in support of Schaudhm's statement 

 (44, p. 95) that the large nucleus ("principal kern") of the megalospheric form 

 results from the massing together of the irregular strands of the microspheric 

 parent. 



