188 QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 



recognised in this condition, they can be traced in the normal 

 lunw, where they are extremely delicate. 



Thread-Cells. — An important paper appears by Eimer 

 (Schultze's ' Archiv,' viii, 281), in which he reports the dis- 

 covery of thread-cells in several species of siliceous sponges, 

 belonging or allied to the family Renierina. He admits that 

 there is something which might almost be called suspicious 

 in a statement which conflicts so decidedly with the accepted 

 zoological classifications, but thinks he has excluded all pos- 

 sibility of error arising from the accidental presence of thread- 

 cells belonging to other organisms, &c. Another important 

 fact is the presence of semen (spermatozoa) in numerous 

 gelatinous, siliceous, and calcareous sponges ; though 

 this point Eimer finds that Hackel had observed simulta- 

 neously in another place. He does not forget to speak of 

 Huxley^s similar observations, made long ago on Tethya, 

 formerly doubted, but now accepted by Hackel ; according 

 to Eimer, however, Huxley, and also Hackel, must have 

 observed spermatozoa in an incomplete state of development. 



