PROTOZOA. 31 



many chambered shell represents a colony. Many natur- 

 alists, however, hold that this is not a colony, but is one 

 zoon with a polythalamous shell. In the case of Difflugia 

 just described, the bud represented another zoon that in 

 this species separates from the parent form, but which in 

 the complex Foraminifera remains attached and makes 

 its own covering. In the arrangement of the Foraminif- 

 era the single forms are given first when this is possible, 

 and afterward the colonial forms which may have arisen 

 from them phylogenetically. 



Saccammina is a simple, hollow, spherical Rhizopod 

 which usually occurs single (PI. 15, fig. i, S. sphaerica 

 M. Sars). Sometimes several shells adhere by their ex- 

 ternal surfaces and the openings remain distinct, as shown 

 in PI. 15, fig. 2, a form which has received the name of 

 Saccammina socialis. This association of zoons where 

 there is no organic connection reminds one of the " so- 

 cieties " of the marine Amoeba obtecta (see p. 25) and 

 of the association of the cytodes of Bathybius. In fig. 3 

 (S. sphaerica} we have such a rude attempt at a colony 

 that it seems to be an initial effort. These zoons are 

 connected by protoplasmic extensions, or stolons. The 

 largest chamber was the primordial one, and was fastened 

 between two stones ; the succeeding zoons then arose as 

 buds which formed their shells in an irregular manner, 

 and the terminal chamber was merely a mass of sand grains 

 with large interstitial openings through which passed the 

 pseudopodia. 



The specimen (No. 16) and PI. 17, figs, i 8, represent 

 Astrorhiza liwicola Sandahl, 1 described by Bessels under 



1 This name was given by Sandahl (Ofvers. Kongl. Vetenskaps- 

 Akad. Forhandl., XIV, p. 299) in 1857, and is retained on account 

 of priority. Brady places Astrorhiza among the Foraminifera. Ac- 

 cording to Sandahl there are many nuclei, but these are figured by 

 him as occurring among the grains of the pseudopodia. an unusual 

 position for nuclei. Bessels, whose observations are more extended, 

 neither figures nor describes a nucleus. Until positive knowledge 

 is obtained we place it provisionally among the Foraminifera. 



