268 CEYLON PEARL OYSTER REPORT. 



PLATE III. 



Fig. 17. Sflrrophytum /jardineri. Transverse section through a ventral mesentery bearing a typical 

 Alcyonarian ovum, x 930. Gam. luc. 



Fig. 18. Sdcrophytum gardinwi. Transverse section showing the unusual occurrence of two young ova 

 on a dorsal mesentery, x 930. Cam. luc. 



Fig. 19. Loboi'hytum jtautijlorum. Transverse section through a siphonozooid just below the surface. 

 All the columnar cells lining the stomodseuni are ciliated, but those of the siphonoglyph are more closely 

 packed and have very long flagella. The endoderm is greatly distorted owing to the presence of 

 zoochlorellae. x 80. 



Fig. 20. Sckrophytwii demstan. Longitudinal section showing stages in development of siphonozooids, 

 Sii, Si-j, Sis, by budding. S'i is the youngest and is formed as a bud from the endodermal canal leading 

 from Sis, and by an aggregation of ectodermal cells to form the stomoda;um, which in the section consists 

 at this stage of only two cells. A plug of mesogltea at this stage closes the mouth aperture. 8i-> is an 

 older bud. The development of the stomodaeiim has advanced, but the mouth aperture is still closed. 

 Si 3 is a siphonozooid which has attained its normal development in this species. The mouth aperture is 

 present and a very rudimentary mesentery (/.) is seen on the right, x 600. 



Fig. 21. Sclerophytuin dentum. Longitudinal section through a developing autozooid. The mesenteries 

 are fairly well developed before the mouth aperture and tentacles are formed. Only one mesentery is 

 indicated in the drawing, x 360. 



Fig. 22. Lobophytum pauciflvrum. Transverse section showing the ciliated communication between two 

 siphonozooids. The endoderm cells differ from those lining the ctelenteron in that they are long, columnar, 

 and are provided with fairly long cilia, x 600. 



Fig. 23. Sclerophytuin densum. Drawing showing the formation of an endodermal canal by the splitting 

 of a solid cord of cells, x 700. 



