MISCELLANEOUS NOTES. 761 



I have rarely if ever seen an oxamplo of so close and exact a resemblance, 

 certainly novor a more deooptivo one. 



To give some idea of the position of repose taken up in the web, which 

 is not likely to be retained after the tumult of its death in spirits, I have 

 made r? roupjh (very rongli I fear) sketches. The two first pair of legs are 

 extended forwards and liexcd, the others are closely apposed to the sides 

 and are indistinguishable without a lense from the body markings. 



In many years of spider collecting and observation I have never seen 

 this species before. 1 should be much obliged if it can be named. I have 

 no work of reference with me and shall be glad if this note is of any value. 



I took this spider in low jungle on a low hill in this district, about 30 

 miles from the sea and 150 feet above it. 



The ant-mimic was on my office table at Gudar in this District. 



C. E. C. FISCHER, i.r.s. 

 Nellore, 22nd November 1917. 



No. XXII.— ON RED SEAWATER. 



Very few of the numerous people who have travelled up and down the 

 Persian Gulf during the last three years can have failed to notice the 

 numerous patches of sea which look as if they had been sprinkled with 

 particles of red sand, or as if they were composed of a thick tomato 

 soup. These patches often extend over many acres, and a ship may pass 

 through such coloured patches for many miles. 



The colour is a rather bright rusty red, and the appearance is due to 

 myriads of unicellular organisms (Protozoa), belonging to the Order 

 DINOFLAGELLATA, of the Class FLAGELLATA. They belong to the 

 genus NOCTILUCA* ; and, like the rest of the Dinoflagellates, they are 

 marked by the presence of a cellulose cuticle Avith transverse and 

 longitudinal grooves, each containing a whip-like thread or flagellum. 



Noctiluca is one of the largest of the Dinoflagellates, and is visible to the 

 naked eye. It varies somewhat in size, averaging about one millimeter 

 (1/25 inch) in diameter. In shape it is globular, but slightly bilobed. It 

 swims freely in the sea by means of great vacuoles within the cell which 

 enable it to float. The protoplasm is situated eccentrically in the cell, 

 and is aggregated into a more or less spherical mass not exceeding about 

 0"05 millimeter (iJo inch) in diameter. From the periphery of this central 

 compact mass of protoplasm branched processes extend across the vacuoles 

 to the colourless cell wall ; the latter is rather thin and very slightly 

 wrinkled, but seems to be tolerably tough. 



The longitudinal groove is not well developed, and its flagellum is so 

 minute that it is difficult to make it out. The other flagellum has the form 

 of a thick tentacle arising from a short transverse groove. This tentacle 

 exhibits constant, slow, worm-like movements in the living organism ; its 

 length corresponds to about half the diameter of the cell, but is somewhat 

 variable. 



The colour of Noctiluca is due to that of the central clump of pro- 

 toplasm ; the fine branched processes Avhich extend from it are almost 

 colourless. As already stated the central mass of protoplasm is only 

 about jj^ inch in diameter ; a fact which enables one to realise the enor- 

 mous number of organisms which must be present to colour the surface 

 of the sea so deeply over such large areas. 



• By some Xaturalif>ts Noctiluca i;? made the type of a Special Order, CF<S TO- 

 FLAGELLALA, 



31 



