316 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3 d See. 



the size and shape of the columnar ectoderm cells, and are 

 found in their best state of preservation in the inner layers 

 of the test, but I have been unable to find a distinct nucleus 

 in any of them. The best occurrence of these cells is 

 shown on the right in fig. 6, and the absence of distinct 

 nuclei is apparent. It must be said, however, that in some 

 places (fig. 10) the nuclei of ectoderm cells that are cer- 

 tainly functionally active have not been differentiated. The 

 distinct nuclei in the proximity of these scattered cells 

 belong to mesodermic cells which may be exercising their 

 phagocytic function. It seems then that ectoderm cells are 

 at times accidentally imbedded in the test, but when there 

 they are no longer able to secrete cellulose and gradually 

 degenerate. 



Most of the mesodermic cells are bladder cells. Occa- 

 sionally, in the innermost layers of the test exceptions are 

 met with in the shape of cells with an abundant granular 

 cytoplasm which entirely fills the cavity of the test they are 

 located in (fig. 7). These, however, are comparatively 

 rare, and as they pass into the outer layers of the test 

 become vacuolated and transformed into typical bladder 

 cells. The latter (figs. 6, 7, 8, 9) are much smaller than 

 the bladder cells in those species of Ascidia where they are 

 so greatly developed, and occupy a much smaller propor- 

 tion of the test. They always present a deeply stained 

 nucleus, but sometimes the cytoplasm and the test cavity 

 which contains it are difficult to make out. The size of the 

 nuclei is quite variable, ranging from that of the ectoderm 

 nuclei to minute, deeply staining bodies one-half or one- 

 third of a micron in diameter. These smaller nuclei seem 

 on the whole to be more frequent in the outer layers. 

 When prepared with most stains the cytoplasm does not 

 seem to extend beyond the wall of the bladder; but a very 

 deep stain, or better still, treatment with Potassium Iodide 

 and Sulphuric Acid brings out quite a number of straight, 

 slender, cytoplasmic processes extending into the test matrix 

 (fig. 8). The size of the cells is much smaller in the 

 densely fibrous parts of the test, and their shape is fusiform 



