IN SACCHAROMYCES. 13 



only a very narrow channel of communication with the parent 

 protoplasmic mass. 



From the nature of this process, it is evident that the envelop- 

 ing membrane is possessed of both elasticity and porosity, 

 varying, no doubt, according to the character of the environment. 



Having demonstrated that the cell-wall is not the hard and 

 shell-like mass that it would at first sight seem to be, the observer 

 experiences little difficulty in realising that it may be readily 

 permeated by nutrient material presented in suitable form, or further 

 by excretitious matter, the retention of which would be injurious. 



EXPLANATION OF PLATE I. 



1. — Sacchai'omyces cerevisice, cultivated in a solution of cane sugar. 

 2. — Cells of the same, as seen under 1/10-in. immersion objective 

 3. — IS. cerevisict, cultivated in a solution of cane sugar with 



ammonia tartrate and ammonia phosphate. 

 4. - Cells stained with methyl violet and aniline green, under 



1/10-in. objective : (a) No, 1 eye-piece ; (6) No. 3 eye-piece. 

 5. — Production of a bud by parent-cell. 

 C. — Cultivation in malt infusion alone, 

 7. — Cultivation in malt infusion with ammonia salts. 

 8. — Cultivation in malt infusion with more of the ammonia salts. 

 9. — Typical cells of S. cerevisice, 1/10 objective, No. 3 eye-piece. 



Fresh-Water Sponges. 

 Mr. Potts, of the Philadelphia Academy of Natural Sciences, 

 states that the order Spongidcs has many more representatives in 

 the fresh waters of Am-erica than has generally been supposed. 

 He recently described before the Academy three species of 

 Spongilla, which he detected in a small stream near Philadelphia. 

 Since then he has found the Spongilla fragilis, of Leidy, plenti- 

 fully in the Schuylkill, below the dam, and a lacustrine form 

 above the dam, and has obtained a very slender green species, 

 which appears creeping along stems of Sp/iagfmm, etc., in a 

 swamp near Absecum, New Jersey, a beautiful species from the 

 Adirondack lakes, another lacustrine form from the lake near the 

 Catskill Mountain House, and four species from an old cellar 

 at Lehigh Gap, Pennsylvania. 



