ACANTHOCYSTIS CHiETOPHOEA. 53 



conditions, as for instance in the absence of the green 

 corpuscles, under which aspect it was named by (xreefE 

 A. pidlida ; it is sometimes seen distended into an 

 ovoid form by numerous large inclusions, which in 

 some cases, at any rate, are ova belonging to a Rotifer 

 of the genus Proales. Stokes watched a struggle in 

 which an ingested Rotifer eventually succeeded in 

 escaping by devouring a portion of the plasma, leaving, 

 however, an egg behind. 



In addition to internal parasites the exterior is 

 often invested by a thick covering of microbes, which, 

 however, do not appear to exercise any deleterious 

 effects. 



The central granule with its radiating lines and the 

 nucleus are usually hidden by the green colouring 

 matter; the nucleus is of a characteristic shape. 



An account of the processes of multiplication in 

 this genus has already been given (p. 11); occa- 

 sionally the animal is found encysted ; the cysts are 

 formed inside the outer investment, and are spherical 

 with a reticulated outer surface which is formed of 

 small discs cemented together, their convex sides 

 being turned outwards. 



Young individuals as small as 10 ijl in diameter occur 

 and have the characteristics of the species. 



2. Acanthocystis erinaceus Penard. 

 (Plate LXXI, fig. 2.) 



Acanthocystis erinaceus 



Penakd Arch. Biol. IX, 1880, p. 455, pi. xxxi, ff. 23-27. 



Penabd Heliozoajres,- 1904, p. 2tl7, fig. 



Wailes & Penard Proc. E. Irish Acad. XXXI, pt. 65, 1911, p. 53. 

 A. alhida 



Pbnaed Arch. Biol. IX, 1889, p. 458, pi. xxxi, ff. 28, 29. 



Body small, spherical ; the outer investment consist- 

 ing of small silicious plates arranged tangentially in a 

 thin layer of plasma having a membranous consistency 

 and radial spines sharply pointed, curved, of moderate 

 length with expanded bases; plasma yellowish in 



