AMONG SIMPLE SAECODE OR&ANISMS. 397 



are much richer in genera and species than the Lobosa ; and we 

 have here, as in the Lohosa, forms in which the shell is a pure ex- 

 cretion from the protoplasm, and others in which it is strengthened 

 by the incorporation of foreign bodies. The first group may be 

 further subdivided into those whose shell is structureless, and 

 those in which it is characterized by the possession of definite 

 sculpture. 



To those in which the test is a simple structureless excretion 

 without the agglutination of foreign particles must be referred 

 the genus Gromia, founded by Dujardin. 



Its more or less spherical or oval test lies close upon the sur- 

 face of the protoplasm-body ; it is membranous, flexible, and in- 

 elastic, and through an opening at one end of its main axis the 

 pseudopodia are emitted and form by their repeated branching 

 and anastomoses a widely extended protoplasm-network. No 

 contractile vacuoles have yet been found. 



Gromia oviformis, on which Dujardin founded his genus, is a 

 marine form. It has been made the subject of a careful study 

 by Max Schultze, who, instead of the single nucleus which almost 

 universally characterizes the freshwater ThalamopJiora, has found 

 in the posterior part of its body numerous clear spherical vesicles 

 filled with granules and regarded by him as nuclei. 



A new species of Gromia, G. granulata, Y. E. Schulze, has been 

 studied by F. E. Schvilze, who found it in fresh water attached to 

 CeratopTiyllum and other water-plants. It is a transparent and 

 colourless species, with its clear protoplasm containing a multitude 

 of strongly refringent granules, which at the periphery are dis- 

 posed at nearly equal intervals, so that when seen through the 

 transparent shell they give to this the appearance of being mi- 

 nutely punctate. Schulze describes a single nucleus lying in the 

 posterior part of the protoplasm. It is a large, clear, spherical 

 body, surrounded by a membrane, and having within it either a 

 moderately large, spherical, strongly refringent nucleolus, or many 

 less distinct dark corpuscles. This is pretty nearly the normal 

 condition of the nucleus in the freshwater Thalamophora, and is 

 so very diff"erent from the numerous vesicle-like bodies described 

 by Max Schultze as nuclei in Gromia oviformis as to lead us to 

 doubt the correctness of attributing to these last the significance 

 of true nuclei. 



The genus Trinema, founded by Dujardin for a freshwater Tha- 

 lamophorous Ehizopod, to which he gave the name of T. acinus, 



