34 



THE TURBELLARIA 



intestine or " stomach," from which more or less numerous caeca 

 which may be more or less branched pass outwards towards the 

 periphery. The caeca are arranged fairly symmetrically in pairs ; 

 and there is with a few specific exceptions always a median 

 unpaired caecum, which passes forwards above the brain. 



cu 



FIG. XVI. Thysanozoon brochii, Grube (after Lang), as an Example of Cotylean Polyclad. 



1. Dorsal view, a, marginal tentacular fold. The body wall is produced into a number 

 of more or less conical papillae, each containing a caecal outgrowth of the intestine. The 

 number of these papillae increases with age. 



2. Ventral view of the anterior end. a, oculiferous tentacular lobes of the margin ; b, 

 mouth leading into the pharyngeal sac ; c, the folded pharynx ; $ , one of the pair of penes 

 carrying a male genital pore at apex ; $ , female pore ; s, sucker. 



3. The marginal tentacular fold of Yungia aurantiaca, seen from above. In addition to 

 the large pair of eyes resting on the brain, the fold is provided with numerous small eyes. 



4. Diagram of the anatomy. The gut is shown only on the left side, and on the right the 

 genital ducts, a, brain ; &, stomach or main gut ; c, network of intestinal caeca ; d, caeca 

 entering dorsal papillae ; h, uterus, from the network on each side a transverse branch goes to 

 the antrum femininum, which opens by the genital pore ($ ) ; e, sperm duct, forming a network, 

 which is connected from side to side by a few transverse branches in front of $ pore ; /, seminal 

 vesicle ; g, penis. 



5. Diagram of part of a transverse section showing the main intestine or stomach (b) 

 with lateral caeca (c) giving off the dorsal caeca (d) which enter the papillae (a) ; c, the muscular 

 coat of the stomach. 



| 



Naturally, in the elongated forms like Prosthiostomum or 

 Eurylepta the " stomach " becomes more tubular and the number 

 of caeca considerable. These caeca always bifurcate and branch, 

 and the branches may even anastomose so as to form a network 

 in some of the Cotylea. In Thysanozoon and Tliysanoplana branches 

 from this network enter the villi on the dorsal surface, but 



