THE NAUTILUS. 23 



reviews Poyarkoff's work and can find no good evidence to 

 substantiate it. 



One fact may be significant to show that the glandular inner 

 wall is not a structure which must be derived from other sources 

 than filaments. In the dorsal part of the gills all of the fila- 

 ments are fused to form a heavy-walled blood sinus. This wall 

 is made up of cells which, in every respect, resemble those of 

 the inner wall of the brood pouch. 



Nutrition of the Embryo. Schereschewsky observes that 

 the embryo in the brood pouch is loathed by a distinct fluid 

 which contains many acidophile granules. This fluid is the 

 secretion of the large gland cells of the inner wall of the pouch. 



Poyarkoff has a different theory. He says, "there are large 

 cells of the inner wall of the brood pouch which serve for the 

 nutrition of the embryo. At a certain time they become de- 

 tached and fall into the lumen of the pouch. Their cytoplasm 

 becomes homogeneous and eosinophile. Their nuclei take a 

 uniform stain. The chromatin granules become almost com- 

 pletely indistinct. The embryo swallows these large cells. I 

 have found these large shells in the intestine of some embryos. 

 Stepanoff (1865) and Ziegler (1885) have noted this mode of 

 nutrition." Poyarkoff further observes that the cells which 

 have thus fallen into the cavity are replaced by leucocytes. 

 Figure 9 is a copy of one of his illustrations. Schereschewsky 

 has reviewed these observations and can find no evidence to 

 justify them. In Calyculina and Sphaerium I have found un- 

 doubted evidence of secretion in the brood pouch. I have 

 found a few cells thrown out into the lumen of the pouch but 

 have considered this a normal phenomenon to be expected 

 among actively secreting cells. As to the cells supposed to have 

 been eaten by the embryo, may these not have been parasites ? 



Sexual Maturity. Gross examination of the gills of Sphae- 

 rium revealed young so large that it was thought probable that 

 these young might themselves be bearing embryos. Examina- 

 tion of microscopic sections proved that such a condition does 

 not exist. The smallest specimen found to contain young was 

 ten millimeters long. This is two millimeters loncer than the 



