272 niLEEHT r. bournk. 



Tig. 24«. — A double concentric spherule from the renal sac. 

 Tig. 25. — A magnified drawing of the area indicated by the reference 

 number 25 in Fiir. 6, showing the intrusive cctoderniic tissue {ec. i.). 



PLATE 22. 



Tig. 26. — Part of a section through the walls of the branchial sac, highly 

 magnified, showing the ineurrent and exciirrcnt branchial chambers and the 

 stigmata. The drawing is made from one of the sections included in the 

 model represented in Fig. IG. 



Fig. 27. — Glandular cells from the epithelium of the stomach (Zeiss -^^^ 

 horn. imm. comp., oc. 4). 



Fig. 28. — The opening of the duct of the subneural gland, highly magnified, 

 showing the ciliated epithelium of the duct. 



Fig. 29. — Outgrowths of the body-wall into the test, showing the pigmented 

 ectodermic epithelium cells, many of which contain yellow granules (highly 

 magnified). 



Fig. 30. — A portion of the section represented in Fig. 25, very highly 

 magnified, showing the intrusive ectodermal ingrowths (cc. i.) at the bases of 

 the arms, and two vascular processes {v. p.). 



F'iG. 31. — A portion of the epithelium from the terminal part of the intes- 

 tine, showing the excretory concretions. 



Fig. 32. — a and d, basophile amoebocytes from the blood-spaces, highly 

 magnified (Zeiss -^^ honi. imm., oc. 8); c and d, empty vesicular amoebocytes 

 from the blood-spaces ; e, a vesicular amcebocyte (trophocytc) with contents. 



Fig. 33. — A portion of the stratified external layer of the contents of the 

 renal sac, showing the formation of the concentrically striated spherules. 



PLATE 23. 

 Fig. 34. — A diagram illustrating the anatomy of Oligotrcma psammitcs. 

 The tissues of the body-wall (ccto- and endoplerome) arc represented in a 

 light shade of blue, the gut in yellow, the test in pink, the ovaries in green, 

 the renal organ and testis iu dili'erent shades of red. The extent of the 

 atrium and right peribrauchial cavity is indicated by a darker shade of blue. 

 The aninuil is represented as dissected from the right side, the right wall oi 

 the branchial sac beiu'j: removed. 



