BEITISH MAEINE TURBELLARIA. 447 



organs is constantly present in sexually mature individuals. 

 When the male products ripen (this species is a distinctly 

 protandrous hermaphrodite) two other pairs (according to 

 V. Graff) arise close to the male genital pore. They differ 

 from the oral pair in three points — their time of appearance, 

 their variability (the hinder pair may be absent), and their 

 disappearance after the shedding of the male products (see 

 V. GraflP, 44, p. 61). The female genital pore lies slightly 

 in front of the centre, the male pore halfway between it and 

 the hinder end. The testes are dorsal in position. The 

 penis is a narrow, cylindrical, muscular tube opening into 

 the short genital atrium, surrounded by radiating accessory 

 glands. The spermatozoa are long ("22 mm.), and consist of 

 a finely granular central portion and hyaline borders, absent, 

 however, on the distinct ''tail." The ova are placed ventrally, 

 and when mature are ovoid, '07 mm. diameter, containing 

 much yellow food-yolk, and surrounded by a delicate mem- 

 brane. Thirty to forty fertilised eggs may be present at one 

 time in a single example. A spermotheca is present. Its 

 neck is produced forwards into a funnel-shaped expansion 

 opening into the female atrium and backwards into the swollen 

 basal portion containing spermatozoa. Round the neck 

 chitinous plates are arranged one over another, the margins of 

 which are thin and colourless, forming the '' mouth-piece." 

 Young specimens of Convoluta paradoxa differ from the 

 adults, to which the foregoing description applies, chiefly in the 

 absence of reflexed marginal lappets, and the small number 

 (five to seven) of symbiotic algse present. 



Habitat. — A littoral species, occurring among seaweeds in 

 tide-pools all round our coast. Berwick Bay (Johnston) ; 

 Firth of Forth (Dalyell) ; among Ceramise, Weymouth 

 (Gosse) ; Skye (Claparede) ; Guernsey (Lankester) ; St. 

 Andrews (Mcintosh) ; Millport (v. Graff) ; Plymouth, Port 

 Erin, Isle of Man (F. W. G.). 



Distribution. — Mediterranean, Adriatic and Black Seas, 

 North Sea^ North Atlantic, coast of Denmark. 



