STRUCTURE OF THE LARVA OP SPONGILLA LAOUSTRIS. 423 



vacuole," but they appear to be present in all cells with vesicular 

 nuclei, and occasionally in the cells with granular nuclei, and 

 even in the collar-cells in the pupa and young sponge. Their 

 occurrence in the last two kinds of cells shows them to have 

 been developed recently from the cells with vesicular nuclei. 



The vacuoles here described behave very differently under 

 the action of various preserving reagents. When the specimen 

 is preserved with absolute alcohol, or a mixture of corrosive 

 sublimate and glacial acetic, or Perenyi's fluid, these en- 

 closures appear as clear vacuoles. When Flemmiiig's fluid is 

 used for a short time some of them are clear while others are 

 black, but when it is used for a long time they are all as black 

 as ink, as they are, also, when the specimens are preserved in 

 Hermann's fluid. Whether as clear vacuoles or as black en- 

 closures they are always circular in section, and equal or even 

 exceed the vesicular nucleus in size (figs. 7, 11, and 11 «). 



When a section of a specimen preserved in Hermann's fluid 

 is subjected to the bleaching action of chlorine, these bodies 

 appear as clear spaces, just as in sections from specimens 

 preserved in either absolute alcohol, or corrosive sublimate 

 and glacial acetic, or Perenyi's fluid. This proves conclu- 

 sively that the clear vacuoles observed in specimens preserved 

 in these reagents correspond to the black enclosures found in 

 material preserved in Hermann's fluid. By stopping the bleach- 

 ing action short of its completion the black enclosures can be 

 seen in different stages of decoloration (fig. 2). 



In sections stained according to Heidenhain's iron hsema- 

 toxylin method they become pale, though with other stains 

 they remain black. In sections of larvae preserved in absolute 

 alcohol, or io bleached sections, the vacuoles were never stained, 

 though a kind of a membrane which surrounded the vacuole 

 always stained with safranin, when followed by gentian violet 

 and iodine, or even with gentian violet alone, as well as with 

 haematoxylin followed by fuchsin S (fig. 2). Whatever substance 

 these vacuoles contained in the liviug condition, it may be 

 concluded that it has been dissolved out of the preserved 

 specimens; and further, the blackening under the action of 



