MESOZOA, 



135 



Metazoan series. He regarded them as intermediate between Protozoa 

 and Metazoa ; but others have remarked on their resemblance to 

 Platyhelminthes, and especially to the sporocysts of certain Flukes. 

 They may perhaps be regarded as precociously reproductive sporocysts. 

 It will be enough here merely to notice four types : 



I. Dicyemidse (type Dicyemd] occur as parasites in Cephalopods ; 



FIG. 63. A. Young Dicyema. 

 After Whitman. B. Female 

 Orthonectid ( Rhopalura giar- 

 dii}. After Julin. 



<?., Ectoderm ; ., inner endoderra cell 

 with nucleus (.); an< 3 embryo (em.). 

 Note the segmentation and the 

 fibrillation supposed to be muscular. 



FIG. 64. SalincBa. 

 After Frenzel. 



1. Longitudinal section 



., anterior;/., pos- 

 terior. 



2. Transverse section. 



the body consists of a ciliated outer layer, enclosing a single multi- 

 nucleate inner cell, within which egg-like germs develop, apparently 

 without fertilisation, into dimorphic embryos (see Fig. 63, A). 



2. Orthonectidre (type Rhopalura] occur as parasites in Turbellarians, 

 Brittle-stars, and Nemerteans ; the body is slightly ringed, and con- 

 sists of a ciliated outer layer, a subjacent sheath of contractile fibres, 

 and an internal mass of cells, among which ova and spermatozoa 

 appear. The sexes are separate and dimorphic (see Fig. 63, B). 



