THE TURBELLARIA 



or more rarely elongated. They are frequently very brightly 

 coloured. 



Lang regards members of this group as representing more 



FIG. XV. A Group of Polyclads. (All after Lang, but 4 and 5.) 



1. Planocera graffi, Lang ; one of the Acotylea, with dorsal tentacles, and eyes at their base. 



2. Leptoplana pallida, Lang ; an Acotylean without tentacles, with a group of eye-spots 

 above the brain. 



3. Leptoplana; ventral view, a, the nearly central mouth; b, the pharyngeal sac; c, the 

 pharynx folded in the sac ; <$ , male pore ; ? , female pore. 



4. Enantia spinifem, v. Gr. ; a peculiar Polyclad, bearing chitinous spines round the 

 margin of the body (after v. Graff), a, mouth; ^, antrum masculinum, receiving the right 

 and left sperm ducts, and opening to the exterior by the male pore ; ? , antrum femininum, 

 receiving the uterine duct, into which open the two uteri (c) ; it is continued backwards to form 

 an "accessory sac" (cZ) or bursa copulatrix ; e, the chitinous spines. 



5. A section through a spine of Enantia. a, ciliated epidermis ; b, epidermal syncytium 

 which secretes the great basal plate of the spine, which consists of solid columns of " chitinoid 

 substance " ; d, a projection of the epidermis consisting of a single cell which secretes the 

 denser part of the spine or hook ; e, the denser part of the spine. 



6. Leptoplana; section through an eye. a, pigmented cup; b, nucleus of pigment cell; 

 c, rods, the modified ends of nerve cells ; d, the nerve cells, which are prolonged into nerve 

 fibres ; e, the optic nerve. 



7. Cydoporus papillosiis, Lang; horizontal section through the margin of the body, a, 

 a caecum giving off a couple of branches (b) which pass outwards to the epidermis ; here 

 each branch communicates by means of a perforated epidermal cell (c) with the exterior ; d, 

 a marginal pore. The intestinal epithelial cells are indicated only by means of the nuclei, 

 as dots ; /, the parenchyma ; g, groups of circular muscle fibres which constrict the caeca at 

 intervals and give rise to the moniliform appearance of these, so usual amongst the Polyclads. 



8. Prosthiostomum Dohrnii, Lang, a, the large everted pharynx, which is exceptional 

 in being tubular, issuing from the anteriorly situated mouth. 



9. Plan of the male organs of Anonymus virilis, Lang, a, marginal eyes, extending all round 

 the body ; bb, the numerous pear-shaped penes and seminal vesicles arranged in two lateral 

 rows ; the small male pore corresponding to each penis is indicated at <J at the point of the 

 penis ; the sperm duct (c) forms a ladder-like network, and communicates with each seminal 

 vesicle, m, mouth ; s, sucker ; ? , female pore receiving the uterus, right and left. 



