590 TRANSACTIONS OF SECTION D. 



Even before the formation of the megalospheres small rounded, faintly staining 

 nuclei can be seen in stained preparations of the emerged protoplasm, and the 

 latter takes a deep flush owing to the presence of minute particles of chromatin. 

 I am not aware that the origiu of these nuclei has been directly observed, but it 

 appears highly probable that they arise by the gathering together about new foci 

 of the staining material distributed through the protoplasm of the microspheric 

 parent. 



The Megalospheric Form. 



When the megalospheres have become formed their protoplasm contains 

 abundance of in-egular chromatin masses, which are at first diffused, and obscure 

 the rounded nucleus near the centre, but I am inclined to think that it is the latter 

 which grows into the large nucleus, the Principal-kern of Schaudinn, which is 

 found throughout the greater part of the life of the megalospheric form. 



As growth proceeds and the number of chambers increases the nucleus moves 

 on from chamber to chamber, becoming greatly constricted as it passes through the 

 narrow passages of communication. It grows pari passu with the growth of the 

 protoplasm. Numbers of nucleoli are contained in it, lying in a reticulum, and the 

 nucleoli appear to increase in number and to decrease in size as growth advances. 

 Here, too, as in the microspheric form, the nucleus appears to give off portions 

 of its substance into the protoplasm, the path along which it has travelled, through 

 the earlier chambers, being strewn with deeply staining particles of irregular size. 

 Towards the later stages the nucleus loses its compact shape and staining power, 

 and ultimately disappears, and multitudes of minute stained bodies may then be 

 detected scattered through the protoplasm. These become aggregated as distinct 

 nuclei, the protoplasm gathers about them, and they divide by karyokinesis. Then 

 follows a second karyokinetic division, and, the protoplasm having divided corre- 

 spondingly, the whole contents of the megalospheric shell emerges as a multitude 

 of minute bitiagellate zoospores, some 4 /n in diameter. 



It so happened that I had been working at the life-history of the Foraminifera 

 at the same time as Schaudinn, though in ignorance of his work.' The results 

 that I have set before you on Puli/stomella were obtained by both of us indepen- 

 dently of one another, though I had not obtained evidence of more than one 

 division of the spore-nuclei or of the number of the flagella of the zoospores. 



The evidence pointed strongly in the direction of the view that the foraminiferal 

 life-history consists of an alternation of generations. While the megalospheric 

 form would, on this hypothesis, arise by a simple vegetative asexual reproduction 

 of the microspheric parent, many considerations seemed to indicate the probability 

 that the microsphere, the initial chamber of the microspheric form, aro.se by the 

 conjugation of zoospores. In addition to the general probability of the occurrence 

 of a sexual stage somewhere in the life-history, the sizes of zoospore and microsphere 

 fitted in with the view that the latter might be formed by the coalescence of 

 two of the former. Again, the fact of the rarity of the microspheric form in com- 

 parison with the megalospheric was comprehensible, on the supposition that, to be 

 able to conjugate, the zoospores must be of different parentage. The point re- 

 mained, however, a matter of inference until three years ago, when Schaudinn 

 published an account of the processes that he had observed,- turning inference 

 into certainty. Premising that chroviidia is the name applied to the fragments of 

 staining material distributed in the protoplasm, I will quote the passage : — 



' With the onset of the cold part of the year I observed that many large Poly- 



' F. Schaudinn, ' Die Fortpflanzung der Foraminiferen, tmd eine neue Art der 

 Kernvermehrung,' Biol. Ccntralblatt, Bd. xiv. N. 4, Feb. 189i. 



' Ueb. d. Dimorphismus der Foraminiferen,' Sitz. Ber. d. Ges. naturf. Fr. 



m Berlin, 1895, N. 5. 



J. J. Lister, ' Contributions to the life-history of the Foraminifera,' Phil. Trans., 

 Vol. 186 B. (1895), p. 401. 



» ' Untersuchungen ub. d. Fortpflanzung einiger Rhizopoden,' Arh. a. d. £ais. 

 Gesiindheitsamte, Bd. six. Heft 3, 1903. 



