THE CONTRACTILE VACUOLE 419 



logical and not to physiological membranes, since these latter cannot 

 be demonstrated in this manner. 



Among the flagellates, Nassonov (1924) found an osmiophilic mem- 

 brane surrounding the vacuole in Chilomonas Paramecium. Haye ( 1930) 

 could distinguish no vacuole wall in the Euglenoidina, but in many other 

 flagellates examined by him distinct walls were visible in stained ma- 

 terial. 



Among the ciliates, morphological membranes are reported in a great 

 variety of organisms by many investigators. Nassonov (1924) reports 

 osmiophilic walls for the vacuoles in Paramecium caudatum, Lionotus 

 joUum, Nassula laterita, Cam panella umhellaria, Epistylis gallea, Zootham- 

 nium arbuscula, and Vorticella sp. Faure-Fremiet (1925) confirmed 

 the findings of Nassonov, using several species of Vorticella, in which 

 osmiophilic walls were observed, even after collapse of the vacuole. 

 Young (1924) concludes from studies on P. caudatum stained with iron 

 hematoxylin that the vacuole system is a permanent and continuous struc- 

 ture. King (1928) arrived at essentially the same conclusion concerning 

 the vesicle-fed system of P. trichium. Wenrich (1926) observed definite 

 vacuole walls in P. trichium stained with Mayer's hemalum or Heiden- 

 hain's iron-alum-hematoxylin. Concerning this Wenrich states (p. 89) : 



It was somewhat surprising to find how distinctly the vacuolar walls showed 

 in fixed and stained specimens. The relative thickness of the wall is note- 

 worthy and it usually appears to be laminated. In sectioned material the walls 

 contained strands of more or less intensely staining material, suggesting 

 the presence of contractile fibers. 



Von Gelei observed osmiophilic walls in P. caudatum (1925, 1928) 

 and in Spathidium giganteum (1935). Haye (1930) found thin vacuole 

 walls in the following forms: Blepharisma undulans, Lionotus fasciola, 

 Ophrydium versatile, Stenlor polymorphus, Spirostomum ainhiguum, 

 Balantidium entozoon, and Isotricha prostoma. Thick walls were ob- 

 served in Campanella, Chilodon, Dogielella, Paramecium, and the Oph- 

 ryoscolecidae. As previously mentioned, Nassonov (1925) examined 

 Chilodon and Dogielella after osmium impregnation and concluded 

 that the vacuoles possess no membranes, but lie directly in the cytoplasm. 

 In these latter organisms, structures considered by Nassonov to be the 

 Golgi apparatus surround the vacuole in such a manner that they may be 

 mistaken for vacuole walls in certain preparations. 



