94 



may be used with advantage. Dr. Donkin has given * a process 

 by means of which Diatoms left by the receding tide on the sea- 

 shore may be separated from the heavier particles, and which 

 seems to have yielded him a rich harvest. The attached and fil- 

 amentous species should always be kept separate from the free ones, 

 in alcohol, as they have to be. treated in a different manner. We 

 must also suit the amount of boiUng, and the strength of the acid, 

 to the species ; some being destroyed by the smallest quantity, 

 and others being ruined by strong acid. Many species, however, 

 (as most of the genus Fhmidaria) require often a minute and a 

 half to two minutes' boiling in strong acid to separate the valves 

 from the connecting membrane. 



Some of the finer marine species are to be looked for in the 

 stomachs of Salpae, Noctiluca, and other minute marine creatures, 

 while the stomachs of most of the mollusks, and those of many 

 crustaceans and fish, will repay examination. The Salpae and 

 Noctiluca are to be procured by skimming the surface of the 

 ocean (more especially in quiet bays and harbors) with a fine 

 muslin net, which may be floated by means of cork or wood, and 

 dragged at the stern of a boat rowed slowly along. When the 

 Noctilucoe are in any quantity, the surface of the ocean will ex- 

 hibit a Uvid light playing upon its surface, especially where it is 

 broken, as on the margin and where the prow of the boat parts it, 

 or the oars disturb it. They are most plentiful in summer, but 

 Diatoms are to be found in them all the year round. Col. Bad- 

 dely found in them, during the winter, such genera as Tricera- 

 tium and Actinocyclus, and during the summer months the fila- 

 mentous forms, as Rhizosolenia ; the same facts, or similar ones, 

 will undoubtedly be observed on our own coast when more atten- 

 tion is paid to this branch of science. I would recommend all 

 who have opportunities of doing so to collect the Noctiluca of any 

 part of our coast and preserve them in alcohol for the Diatoms 

 they contain. The Ascidia^ and Holothurice also yield rich har- 

 vests of Diatoms, and when they come from a distance, as from 

 the Pacific Ocean, where they are plentiful, are extremely inter- 

 esting. The contents of the stomachs of the Noctilucae may be 

 simply washed in distilled water and preserved in alcohol ; those 

 of Salpai and Ascidia? should be cleaned with nitric acid, but the 



* Mic. Soc. Trans. Vol. VI. p. 12. 



