144 J. J. LISTER. 



suggests that it was formed of two equal and incompletely fused 

 or possibly incompletely separated spheres, to which apparently 

 the nuclei correspond. In one specimen with seventeen 

 chambers the nucleus is represented by seven pieces, distributed 

 through the first seven chambers ; in this case the megalosphere 

 is very large (160 x 134 yu.). There is no irregularity or peculi- 

 arity of growth in the remaining seventeen specimens. In two 

 of them three nuclei are present, and two in the remainder. 



The nuclei, when more than one are present, are generally 

 about equal in size, and usually, though not always, situated in 

 the same or adjoining chambers. The size of their nucleoli may 

 be about the same, or the nuclei may present a marked differ- 

 ence in this respect. Thus, in one case in which two nuclei are 

 present in one chamber, one contains vacuolated nucleoli, of 3 /* 

 diameter, the other is crowded with minute nucleoli of a 

 diameter of 1 fi. Two other cases presented a similar contrast. 



The significance of the presence of more than one large 

 nucleus in a megalospheric form will be discussed below. 



Reproductive Phase. Formation of Zoospores. — Among 

 Polystomellas collected between the end of March and the end 

 of May, 1893, specimens are not uncommon in which the large 

 nucleus is absent altogether. As an indication of the frequency 

 with which these specimens occur, I may mention that among 

 thirty-eight examples of megalospheric forms, collected on April 

 30, and stained and mounted without any selection, eight have 

 no large nucleus. 



These specimens generally present another conspicuous 

 feature, namely, that the megalosphere in many cases communi- 

 cates by broad channels with the adjacent chambers of the 

 inner whorl, in addition to the usual communication between 

 successive chambers. In the same way communications are 

 found between the peripheral parts of the chambers of the inner 

 whorl and those of the outer (fig. 32, a). 



When treated with picro-carmine such specimens frequently 

 stain a more or less deep pink colour throughout, though in 

 some cases they remain pale. 



Sections of these specimens generally show minute nuclei 



