SPICULA OF THE DORIDID^. 



and ultimately become united, the result being a slender spiculum with large rounded ex- 

 tremities. The spiculum then goes on thickening until it completely mis the vesicle, and puts 

 on the mature nodulous appearance. Afterwards the vesicle becomes indistinct, or perhaps 

 entirely disappears. 



Fig. 1. Spicula as arranged in Doris pilosa. 



2. „ „ Doris aspera. 



3. „ „ Goniodoris nodosa. 



4. ,, „ dorsal tentacles of ditto. 



5. „ „ Triopa claviger. 



6. 7, 8, 9, 10, 11. Spicula of Thecacera pennigera in various stages of growth: 



a, vesicle ; b, spiculum. 



