ON PHTMOSOMA VARIANS. 25 



DESCRIPTION OF PLATES I, II, III, and IV,^ 



Illustrating Mr. Arthur E. Shipley's paper '"^On Phymo- 

 soma varians/' 



PLATE I. 



Fig. 1. — A semi-diagrammatic view of the anterior end of Phymosoma 

 varians. Tlie introvert is everted and the tentacular crown expanded. The 

 collar is not extended and lies at the base of the head. Only two rows of 

 hooks are shown. 



Fig. 2. — A semi-diagrammatic view of the closed vascular system and 

 nervous system, showing their relation to the alimentary canal. The vascular 

 system shows the three parts, the lophophoral, the lower lip, and the dorsal 

 blood-vessel. The latter communicates with the lophophoral in the middle 

 line, and just at this point the sinus round the brain is given off. The brain 

 is relatively too small. The three main nerves are shown, and the circular 

 nerves which run in the skin. The oesophagus is cut off abruptly in front in 

 order to display the vascular ring. 



Fig. 3. — View of a Ph. varians which has been opened along the 

 median dorsal line. The introvert is retracted, the true anterior end of the 

 body being where the eye-spots lie. Here and there patches of skin are 

 seen which bear papillae. 



PLATE II. 



Fig. 4. — A median longitudinal section through the head. The introvert 

 is retracted, and the collar expanded until it encloses the whole head. The 

 section is not quite in the middle line, or the lip on the dorsal surface 

 would not be shown, cf. Fig. 6. The brain is cut through that part which is 

 continuous with the ectoderm. 



Fig. 5. — A transverse section through the tentacles : the introvert is re- 

 tracted. The tentacles show the ciliated groove on the outer surface, the 

 pigmented epithelium in the inner, and the vascular spaces and tentacular 

 nerves. 



Fig. 6, — A transverse section through the base of the lophophor and lower 

 lip, just where the two fuse dorsally, the introvert is retracted. The skeletal 

 tissue is shown in the lip, which is ciliated all round. 



Fig. 7. — An oblique transverse section through the base of the lophophor, 

 showing the blood-space ; and in the centre some of the wrinkled pigmented 

 tissue of the praeoral lobe. The introvert is everted. 



' 1 am indebted to Mr. Weldon for the following figures : — Nos, 1, 7, 10, 

 12, 14, 15, IG, 20,21, 23, and 27. 



