94 



MESOZOA 



CHAP. 



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- 

 fusoriform, 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. 

 Dicyema typus van Ben. 

 D. clausianum van Ben. 

 D. microcephalum Whit. 

 D. moschatum Whit. 

 D. macrocephalum van Ben. 



D. truncation Whit. 



D. schultzianum van Ben. 



Dicyemennea eledones Wag. 



I). miilleri Clap. . 



D. gracile Wag. 



Conocyema polymorphum van Ben. 



Host. 

 Octopus vulgaris. 

 0. macropus. 

 0. de Filippi. 

 Eledone moschata. 

 Sepiola rondelelii. 

 Rossia macrosoma, Sepia 



elegans, S. officinalis. 

 S. biseralis, Octopus vulgaris. 

 Eledone moschata, E. aldro- 



vandi. 

 E. cirrosa. ' 

 Sepia officinalis. 

 S. officinalis, Octopus vulgaris. 



Orthonectida. 2 Two species of Orthonectids are fairly well 

 known, Ehopalura giardii Metschn. from Amphiura squamata, 

 and R. 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. Metschnikoff 

 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 Amphiura, 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. Ncapel, Bd. iv. ; see also Braun, in Bronn's 

 Thierrcich, Bd. iv. p. 253. 



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



3 Giard, "La Castration parasitaire," Bull. Sci. d. France et de Belgiquc, 3 ser. 

 i. 1888, p. 12. 



