188 F. W. GAMBLE, B.SC. 



long (one-fourth the length of the body), cylindrical, and muscular. 

 The otolith has a distinct central portion, and is radially striated. 

 The two eyes are large, and provided each with a lens. The common 

 genital pore lies at the hinder end of the body. It leads into a 

 ciliated, muscular, narrow atrium, which is an invagination of the 

 hinder extremity. Testes rounded, scattered. Vesicula seminalis 

 spherical, opening into the pyriform muscular penis enclosed in its 

 sheath. These organs lie at the front end of the genital atrium. The 

 spermatozoa when mature are broad and thick, tapering at either end, 

 the head filament shorter than the tail. Ova occur in two lateral 

 rows, sometimes those of one side being more developed than those of 

 the other (v. Graff). 



Habitat. — This active yellow form is not uncommon between 

 tide-marks in Plymouth Sound (F. W. G.). This is, I believe, the 

 first record of its occurrence north of the Mediterranean. 



Distribution. — Trieste, Naples, Messina (v. Graff), Lesina (Schmidt, 

 28), Sebastopol (Uljanin, 41). 



Genus 2. — Monoporus, v. Graff (56) 



(= Proporus, Schmidt, 28). 



Proporidce with spermotheca. 

 2. Monoporus rubropunctatus (0. Schmidt, 28). 



Length 1 mm. Body ellipsoidal with rounded extremities. Colour 

 white, the central parenchyma brown, owing to the presence of 

 coloured vacuoles and food-particles. The epidermis contains clavate 

 rhabdites, the thickened outer ends of which project beyond the 

 surface. The mouth is mid- ventral, leading into a very short simple 

 pharynx; the "terminal mouth" of earlier descriptions being, accord- 

 ing to v. Graff (5C, p. 57), the opening of the "frontal organ." The 

 eyes lie right and left close to the anterior end. They are placed in 

 the epidermis, and consist of polygonal pigment masses of a brilliant 

 carmine colour. In his recent accounts of the " Acoela " v. Graff gives 

 some interesting additions to our knowledge of the genital organs. 

 The genital pore is single. The testes are compact as in no other 

 Acoelous form. The vasa deferentia are merely their posterior prolonga- 

 tions. The oviducts are continuous with the epithelial lining of the 



