HARDWICKE'S SCIENCE-GOSSIP. 



241 



GRAPHIC MICROSCOPY. 



By E. T. DRAPER. 



NO. XXIII. — POLYSIPHONIA FASTIGIATA. 



N most of the larger 

 littoral algae, but 

 rarely beyond low- 

 water mark, may be 

 found the delicate 

 and elegant parasi- 

 tical Polysiphonia 

 fastigiata ; it grows 

 abundantly on the 

 fronds of Fitats 

 nodosus, and often 

 entirely covers the 

 long thong - like 

 stems of Fucks 

 vesictilo sus. Al- 

 though common, and 

 apparently uninvit- 

 ing as an object of 

 beauty, the micro- 

 scope reveals its 

 extreme elegance. It is discovered forming dense 

 globular tufts two or three inches long, about the 

 thickness of a horse hair at the base, expanding in 

 parallel branches pointing upwards, somewhat rigid. 

 Microscopically, the frond is found to be fili- 

 form, and articulated, repeatedly forked, marked 

 externally with striae, interrupted at the joints, and 

 generally the structure is disposed in a series round a 

 central cylindrical internal cavity ; the colour brown- 

 pink— purple-black when dry. Although the mode 

 of propagation has until recently been somewhat 

 obscure, it is ascertained that there are two kinds of 

 fructification, in distinct plants. Tetraspores which 

 at maturity divide into parts, generally four, or more ; 

 and antheridia, oblong bodies, rounded at the extre- 

 mities, produced in fascicles on the summits of the 

 ramuli, and subdivided into parts. The drawing 

 shows the apices of a frond with these reproductive 

 organs. They are so extremely abundant in the early 

 spring months, as to give a very conspicuous yellow 

 colour to the tufts on which they are produced. 

 Minute marine algse, for microscopical observation 

 No. 251. — November 1885. 



and preparation may be cultivated, or rather kept 

 in a growing condition for a few weeks in small 

 vases of sea-water, in a cool and shady position, 

 under an equable temperature. It is of importance 

 that the plants should be attached to a portion of 

 the substance on which they are found growing ; for 

 permanent preservation, the lace-like fragment should 

 be floated on fresh water, lifted carefully on the usual 

 glass slip, well drained and immersed in glycerine 

 jelly under a thin cover ; no pressure should be 

 used. Dry specimens are mounted, but they rarely 

 exhibit the integrity or delicate features of the 

 fructification. 

 Crouch End. 



ON MIMICRY IN DIPTERA. 



WHEN will some of our entomologists who have 

 collected and studied nearly every Lepidop- 

 terous insect known to inhabit Great Britain, devote 

 even a small amount of attention to the other orders 

 of insects ? The Coleoptera certainly have received 

 a fair amount of attention, but the Diptera have 

 been sadly neglected. 



And this unpopularity is scarcely deserved by them, 

 for albeit they do not possess the brilliant colouring 

 and large dimensions of some butterflies, many of 

 them are extremely elegant ; while their points of 

 interest will be found to be almost more varied and 

 more striking than those of the Lepidoptera. 



Any who would take the trouble to catch and 

 pin out the Diptera found in their neighbourhood 

 might possibly discover new habitats, if not new 

 species ; in any case, such a collection would greatly 

 assist our knowledge of the distribution of the various 

 species. 



Those who travel miles to find a rare moth are 

 usually only going over old ground that has been 

 visited by scores of collectors bent on the same 

 errand, and instead of increasing our knowledge of 

 the insects, are only lending their small aid to the 

 extermination of the species. 



u 



