530 OLWEN M. REES. 



At the point where the tentacle joins on to the peristome the tissues are 

 much thicker, the nerve layer is much broader, and there is a stronger 

 ectodermal muscle. The mesogloea is thicker and has a plaited appear- 

 ance. The cells of the endoderm have a colunmar structure, but the 

 inner margin of that region appears to be very irregular ; some of the 

 cells project farther into the cavity than others. 



Zooxanthelles are present in the endoderm. 



Sagartia sphyrodeta (Gosse). 



The specimen described here was sent from Plymouth. It was killed 

 expanded and preserved in formalin. It was left for a considerable time 

 before being examined, so that the structure of the tissues was in many 

 places obliterated, and the colouring could not be verified. The tentacles 

 are arranged on an octamerous plan : 8+8+16+32 = 64. This number 

 of tentacles is usually found in Plymouth specimens. Gosse found 

 only 48, arranged thus : 8+8+16+16 ; and Fisher, in 1874, gives 

 8+8+16+32+64=128. 



Measurements were taken from the preserved specimen as follows : — 



Diameter of tentacular crown =18 mm. 



,, ,, disk =7 mm. 



Length of primary tentacles =5 to 6 mm. 



„ ,, outer ,, =3 mm. 



Diameter of pedal disk =6 mm. 



Height of column =4 mm. 



The body-wall is weak, the mesogloea forming a very thin, fibrous 

 strand between the endoderm and the ectoderm. The endoderm is about 

 half the thickness of the ectoderm. Near the cinclides the ectoderm is 

 very much swollen in each case ; these openings are few and are found 

 near the upper part of the column. The acontia have large gland cells, 

 nematocysts, and granules. 



The sphincter muscle (Fig. 6) is in shape very much like that figured 

 for S. carlgreni by Haddon and Duerden in Trans. R.D.S., 1896. It is not 

 nearly so long as that of S. milmani, and the cavities are more numerous 

 than in the sphincter of S. carlgreni. 



The mesenteries (Fig. 7) are very weak, the retractor muscle forms a 

 shallow cushion, and the parieto-basilar muscle is very long and thin. 

 The endoderm contains numerous oval gland cells, which are full of 

 deeply stained granules. 



The oesophagus has one groove ; the folds in the ectoderm of the wall 



