STRUCTURE OF THE LARVA OF SPONftTLLA LACUSTRIS. 425 



As has been stated already, they are present in all the types, 

 though they are far more numerous in types A and B than in 

 types C and D. In types A and B they show great affinity for 

 bleu de Lyon, while in types C and D the substance which dis- 

 played the above, affinity for the blue colour seems to have been 

 used up almost completely, so that had they not been observed 

 in types A and B they would have been probably overlooked in 

 the other two types, owing to the difficulty with which they are 

 stained. They can be stained, however, with bleu de Lyon in 

 these types as well as in types A and B, provided the specimens 

 have been preserved in absolute alcohol, or in corrosive subli- 

 mate and glacial acetic (fig. 6 a). But if they have been pre- 

 served in Hermann^s or Flemming's fluid they often display 

 an affinity for the carmine rather than for the bleu de Lyon, 

 and are consequently stained red (fig. 7). 



Appendix B. 



On the Origin of the Cell Groups found in 

 Types B and C. 



The groups, the origin of which will be described in this 

 appendix, must have originated from one or other of the three 

 kinds of cells described in type A. They may have been 

 derived from the flagellated cells by immigration, or from the 

 cells with vesicular nuclei, either directly by division or frag- 

 mentation, or indirectly by passing through the intermediate 

 condition of the cells with granular nuclei. 



There are two points in favour of the view that they have 

 been derived from the flagellated cells by immigration. In the 

 first place, the nuclei of the cell groups on the one hand and of 

 the flagellated cells on the other are almost identical both in 

 structure and size, while in both these respects they diff'er 

 widely from the granular nuclei. In the second place, the size 

 of the cells of the incompletely divided groups agrees with 

 that of the flagellated cells rather than of any others. But, on 

 the other hand, there are several points which go against this 



