66 THE FORAMINIFERA 



between the retral processes, before mentioned as visible on the 

 surface of the test (Fig. 7). The short canals springing from the 

 meridional canals of the inner convolutions open into the chambers 

 of the convolution next external. The canal system is thus in 

 communication with the chambers. In addition to the meridional 

 canals, other branches spring from the spiral canals and pass to 

 the surface in the umbilical region, traversing the thick mass 

 of canalicular skeleton there deposited. 



The course of the spiral canals is in some cases irregular, and 

 they often break up into a network of sinuses. In the small 

 specimen shown in Fig. 11, c, the spiral canal of one side is seen 

 close to its origin, and a meridional canal is shown, between the 

 second and third chambers ; but I have been unable to trace the 

 points of origin of the spiral canals. 



On treating a batch of decalcified specimens with a stain such 

 as picrocarmine, the nuclei appear, and again the two sets of 

 individuals come into marked contrast. The megalospheric form 

 possesses a single large nucleus, while the microspheric form 

 possesses a number of small nuclei, distributed through its 

 chambers (Fig. 8). 



In Polystomella crispa, then, the megalospheric individuals 

 are numerous, they have a large central chamber and a single 

 large nucleus ; while the microspheric individuals are com- 

 paratively scarce, they have a small central chamber, and many 

 nuclei. 



The existence of the phenomenon of dimorphism being verified, 

 the question arises : How are the two forms related ? 



For an answer to this question we turn to the life-history, and 

 what is known on this head will now be given. 



LIFE -HISTORY OF POLYSTOMELLA CRISPA The Microspheric 

 Form. The youngest specimens of this form that have been met 

 with already contained many nuclei. Thus in one, described by 

 Schaudinn (44, p. 92), with nine chambers, twenty-eight nuclei 

 were present. 



The nuclei are at first homogeneous bodies, but as the animals 

 grow nucleoli make their appearances. The nuclei are irregularly 

 scattered through the protoplasm, though they are not found in 

 the terminal chambers. They are often grouped in pairs, and 

 there is good evidence that they multiply by simple division (20, 

 p. 419). The nuclei in the larger chambers are larger than those 

 in the small chambers near the centre, and they, may attain a 

 diameter of 40-50 ^. 



In addition to these rounded nuclei, there are generally present 

 in the protoplasm of the microspheric form abundant irregular 

 strands of darkly staining substance, which are apparently given 

 off by the nuclei. In some cases no definite nuclei are visible 



