CHAPTER IV 



MESOZOA 



DICYEMIDAE STRUCTURE REPRODUCTION OCCURRENCE : 



ORTHONECTIDAE OCCURRENCE STRUCTURE : TRICHOPLAX : 



SALINELLA. 



The Mesozoa are an obscure group, the position of which in the 

 animal kingdom is still doubtful. The 

 name Mesozoa was given to the group by 

 its discoverer, E. van Beneden, 1 as he 

 concluded that they were intermediate 

 between the Protozoa and the higher 

 Invertebrates. Eecent authors, however, 

 have called attention to the resemblance 

 existing between them and the " sporo- 

 cysts " of Trematodes, and though we 

 still are ignorant of certain important 

 points in their life-histories, the Mesozoa 

 are most conveniently (and probably 

 rightly) considered as an appendix to the 

 Platyhelminthes. 



The animals composing this group are 

 minute and parasitic, and are composed 



Fig 45.-A,B,c, stages in the of a sma n num ber of cells. They may be 



development of the vermi- . . . . 



form larva in Dicyema typus divided into two families: the Dicyemidae, 



Beneden') l^cuStt^ which occur exclusively in the kidneys 

 gc, germinal cell ; n, nucleus of certain Cephalopods (cuttle-fish); and 



of endodermal cell. ^ Q rthonectidae> which live in the brittle . 



star Amphiura squamata, the Nemertine Nemertes lacteus, or the 

 1 Ed. van Beneden, Bull. Acad. Roy. Belgique, 1876, p. 35. 



