206 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



the auimal becomes free. It is probably referable to the Platjctenea. 

 This is indicated by the covering of the ventral surface with ciliated 

 epithelium and the profuse foldings in the central region of that surface. 

 The ventral surface may have arisen, as in Cmloplana, by a turning out 



Advanced stage of Gastrodes parasiticmn Korotneff, which has changed 

 from a more flattened to a hemispherical shape on liberation from 

 the host. X 50. 



c, comb-plates; s., aboral sense-organ; t.b., tentacle basis; w.c, 

 meridional canal ; ph.c, pharyngeal canal ; t., tentacle, 



of the pharynx. Moreover the oesophagus is well differentiated, the 

 meridional canal exhibits signs — though slight — of branching, and the 

 infundibular canal is obliterated. J. A. T. 



Protozoa. 



Influence of Environment on Arcella. — Robert W. Hegner 

 {Journ. Ejyer. Zooh, 11)11), 29, 427-41, 7 figs.). AVhen specimens of 

 Arcella dentata are underfed, the interval between successive divisions 

 increases from an average of 2 • 5 days to about 4 ; the shell decreases 

 in diameter on the average 2 '08 units of 4*;^ /a each ; the spine number 

 slightly decreases. The offspring are normal when given abundant 

 food. In a medium containing 1 drop of sodium silicate to 100 cc. of 

 water A. dentata grows and reproduces ; the fission rate decreases 

 as above ; the size of the progeny produced in the solution is reduced ; 

 the spines disap])ear; the colour, which becomes brown in a normal 

 medium, remains a pale greenish yellow. Specimens reared in this 



