222 ARTHUR EARLAXD UN THE FORAMINIFERA OF 



Probably not less than 10 per cent, of all the specimens show 

 more or less evidence of this phenomenon. 



From the large number of specimens observed at Bognor it is 

 possible to add several observations to the foregoing description. 

 I have noted : — 



1. The two specimens are rarely identical in size, and some- 

 times the disparity is very noticeable. 



2. The apertures do not necessarily coincide, and in a great 

 number of instances the edges overlap, or the smaller specimen 

 is set to one side of the vertical axis of the larger specimen. 



3. Sometimes three, four, or more specimens are united in 

 a more or less irregular manner (Plate 12, Fig. 7). 



4. That in many instances the two specimens represent 

 varying types, one being of the outspread D. parisiensis, while 

 the other comes nearer to the more compact D wrightii. 



After the fusion of the protoplasm and the formation of the 

 young brood within the cavities of the united parent shells, it 

 appears that the shell substance by which the parents are united 

 is again absorbed, and that separation of the parent shells ensues, 

 the young tests escaping through the large opening produced by 

 the absorption of the parent's base. Such separated specimens 

 are of frequent occurrence, and one is represented in Plate 12, 

 Fig. 5. It is noticeable that the whole of the internal septa have 

 been absorbed, their position being marked only by septal lines 

 on the inner wall of the test. The test thus resembles a hollow 

 cone, the whole of the cavity being available for the growth of 

 the young brood while they remain in the cavity. Probably the 

 carbonate of lime thus obtained from the absorption of the septa 

 and basal wall is utilised for the secretion of the monothalamous 

 shells of the young brood. I have noted this complete absorption 



however, of infrequent occurrence except in the genera Textularia 

 (T. folium, P. & J.) and Dueorbina. 



Chapman, in his book The Foraminifera (Longmans, Green & Co., 

 1902, p. 31), quotes a description of the process of plastogamy as 

 observed by Schaudinn in a species of Dueorbina. " The flat or inferior 

 faces of the tests are brought together with the apertures coinciding. 

 The walls of the last-formed chambers are sometimes resorbed, and an 

 i ndosing shell made around the space between the tests. Then follows the 

 breaking up of the nuclei and the formation of embryonic young, which 

 speedily form their own investment to the extent of two or three chambers 

 before breaking away from the enclosing shell."— Schaudinn, " Ueber 

 rinstogamie bei Foram.," Sitz. Gesellsch. naturforseh . Freunde, 1895, No. 10. 



