.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 :— 
1. Dicyemidz (type Dzcyema) occur as parasites in Cephalopods ; 
Fic. 63.—A. Young Décyema.— Fic. 64.—Salinella. — 
After Whitman. 3B. Female After Frenzel. 
Orthonectid (Ahopalura giar- Pee en eee 
dzz).—-After Julin. = stron e ‘ pape 
terior. 
¢., Ectoderm ; e7., inner endoderm cell 
with nucleus (z.); and embryo (e77.). 
Note the segmentation and the 
fibrillation supposed to be muscular. 
z. 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. Orthonectide (type RAopalura) 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). 
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