128 BRITISH FRESHWATER RHIZOPODA. 







complete control as if the threads were permanently 

 differentiated limbs acted on by particular muscles, 

 and directed in their movements by nervous agency. 

 Threads dissolve their connection and are withdrawn ; 

 new ones are formed and establish other connections ; 

 they bend; they contract into a spiral; they occasionally 

 move like the lashing of a whip, and indeed produce 

 almost every conceivable variety of motion. Not 

 unfrequently spindle-like accumulations of protoplasm 

 occur in the course of the pseudopodal threads. Some- 

 times, through the conjunction and spreading of several 

 of the latter together, islet-like expansions occur, and 

 become the centres of secondary nets. 



" The pseudopodal extensions of Gromia consist of 

 pale granular protoplasm with coarser and more 

 defined granules. The latter are observed to be in 

 incessant motion along the course of the threads, 

 flowing in opposite directions in all except those of the 

 greatest delicacy. In the larger threads, the granules 

 are immersed and near together; in the smallest 

 threads, they are in single rows, more or less widely 

 separated, and thicker than the threads, so that these 

 appear like strings of minute beads. . . . Besides 

 the granules, minute vacuoles often make their appear- 

 ance along the course of the pseudopods. Some of 

 these seem to be of the character of contractile vesicles, 

 starting as mere points, slowly enlarging, and then 

 collapsing." 



Genus 45. MICROGROMIA Hertwig .& Lesser, 1874. 



Arcella (pars) FKESENIUS in Abh.- senekenb. nat. Ges. II 



(1858), p. 219. 

 Cystophrys (pars) ARCHER in Qrt. Jrn. Micr. Sci. (N. s.) IX 



(1869), p. 259. 

 Gromia (pars) ARCHER in Qrt. Jrn. Micr. Sci. (N. s.) IX 



(1869), p. 322. 

 Microgromia HERTWIG & LESSER in Arch. mikr. Anat. X 



(1874), Suppl., p. 1. 



