ORTHONECTIDAE 



95 



Rhopcdura giardii is of distinct sexes. Either males or 

 females are found in one Amphiura. Two kinds of females, 

 flattened unsegmented, and cylindrical segmented forms, are 

 known. They consist of a ciliated ectodermal layer enclosing an 

 endodernml mass of eggs, between which is a fibrillar layer 

 usually considered to be of a muscular nature. The cylindrical 

 female gives rise to eggs which develop, probably exclusively, into 



Fig 



47. Rhopalura 

 giardii Metschn. 

 (from the brittle-star 

 Amphiura squa- 

 mata). 6, Full - 

 grown male ( x 800) ; 

 9 w flattened form 

 of female ( x 510) ; 

 ? 2 , cylindrical 

 female ( x 510). 

 (After Julin. ) 



males. The flattened female produces eggs from which females alone 

 arise, though the origin of the two forms of this sex is not well 

 ascertained. The males contain spermatozoa which fertilise the 

 eggs of the cylindrical female, whereas the ova of the flat form 

 probably develop parthenogenetically. 



Trichoplax. 1 This anomalous animal has only been found 

 in aquaria, originally in the marine aquarium at Graz by 

 1 Schulze, Abh. AJcad. Berlin, 1891, p. 1. 



