BRITISH MARINE TURBELLARIA. 189 



ovary, and unite to form a vagina. Opening into this vagina is a 

 spermotheca, the duct of which is slightly chitinised. 



Habitat. — Among littoral alga), Plymouth Sound (F. W. G ). 



Distribution. — Naples, Trieste, Dalmatian Islands (v. Graff, 55), 

 Lesina (Schmidt, 28). 



Family APHANOSTOMID.E. 



Acala with two genital apertures, the female pore placed in front of the 

 male. A spermotheca present. 



Genus 3. — Aphanostoma, Oersted (21). 

 Spermotheca unarmed. 



3. Aphanostoma diversicolor, Oersted (21). 



Length -75 — 1 mm. Body somewhat fusiform, tapering gradually 

 forward from the posterior third, more rapidly backwards to the hinder 

 end. The colour (which is variable in amount and inteusity) is due to 

 violet pigment-cells and yellow vacuoles in the parenchyma. These are 

 usually disposed in a characteristic way. The yellow pigment is 

 present at the anterior end, and extends a short distance backwards 

 on each side, enclosing the violet pigment which occupies the mediau 

 part of the body as far back as the limit of the anterior third. 

 A small patch also occurs at the extreme hinder extremity. The 

 violet pigment cells are capable of altering their shape according to 

 the state of contraction of the body. Their most characteristic form 

 is that of a U, the curved portion being much thicker than the long 

 slender processes. 



The mouth is almost mid-ventral. It leads into a funnel-shaped 

 pharynx. Two genital apertures are present. The male pore lies a 

 short distance in front of the hinder end, the female pore still further 

 forward. The conical penis encloses a veslcula seminalis in its proximal 

 part. The ovaries extend throughout the greater part of the body. 

 A spermotheca, possessing intrinsic and extrinsic muscles, opens into 

 the vagina. The epithelium of its duct (according to v. Graff) secretes 

 a cuticle. 



