94 MESOZOA 



bogen." Other individuals which produce a more elongated 

 larva ("vermiform larva," Fig. 45) are called " Nematogens," 

 and Whitman has described a third kind, which produce first in- 

 fusoriforin, and then vermiform, larvae (Secondary Nematogens). 1 

 The occurrence of the known species of Dicyemids (a group 

 which has not been investigated on our coasts) is as follows : 



Species. Host. 



Dicyema typtis van Ben. . . Octopus vulyaris. 



D. clausianum van Ben. . . . 0. inacropus. 



D. microcephalum Whit. . 0. de Filippi. 



D. moschatum Whit. .... Elcdonemosch<it. 



D. macrocephalum van Ben. . . . Sepiola rondeletii. 



, I71 . ( Rossia mncrosoma. S?)>i<( 



D. truncatum Whit ..... < . _ .' . '. 



( deyans, .S. qfficinaiia. 



D. schultzianum van Ben. . . /S'. biseralis, Octopus rulyttris. 



,_. . , , ,, T ( Eledonc vioschata, E, ulttni- 



Dicyemennea eledones Wag. . . . < . / 



D. miilleri Clap. . . . . E. cirrosn. 



D. (jracile Wag. ..... Sepia ojficinalis. 



Conocyema polymorphum vaii Ben. . . >S. offfcinalis, Octopus 



Orthonectida. 2 Two species of Orthonectids are fairly well 

 known, Rhopalura giardii Metschn. from Ampliiura squnmnta, 

 and E. intoshii Metschn. from Nemertes lacteus. The latter appears 

 to be very rare, the former occurring in 2 to 5 per cent of the 

 number of hosts examined. The parasites occur in a granular 

 " plasmodium," the nature of which is uncertain. Metsclmikoff 

 regards it as formed by the Orthonectids, and he considers that 

 the cellular envelope, by which it is sometimes enclosed, is 

 developed from the neighbouring tissue of the host. These 

 granular, sometimes nucleated, plasmodial masses, which can 

 perform active amoeboid movements in sea-water, occur attached 

 to the ventral part of the body-cavity of Ampliiura, and between 

 the gut-branches and body-wall in Nemertes. Should these hosts 

 be infected by great numbers of the Orthonectids, their sexual 

 organs degenerate (as is the case with pond-snails attacked by 

 sporocysts 3 ), and it is possible that the remains of these organs 

 may constitute the " plasmodia " (Braun). 



1 Whitman, Miltheil. Zool. Stat. Neapel, Bd. iv. ; see also Braun, in Bronii's 

 Thicrrcich, Bd. iv. p. 253. 



2 Braun, loc. cit. p. 281 (with literature). 



3 Giard, " La Castration }arasitaire," Bull. Sci. d. France et de Belyiquc, 3 ser. 

 i. 1888, p. 12. 



