220 



HARDWICKE'S SCIENCE-GOSSIP. 



[Oct. 1, 1869. 



body is suddenly suffused with a deep pinkish glow. 

 Before we have time to recover from our surprise this 

 colour fades, and a beautiful blue takes its place as 

 rapidly as a blush sometimes suffuses a delicate 

 cheek. The blue, perhaps, is succeeded by a green, 

 and then the whole body becomes pink again. One 

 can hardly conceive anything more beautiful than 

 this rapid play of colours, which is produced by the 

 successive distension of sets of little sacs con- 

 taining fluids of different colours, which are 

 situated under the skin. 



The cuttle-fish is also furnished with a bag con- 

 taining an inky fluid, which, when the animal is 



Fig. 1/2. Loligo vulgaris, with its feather. 



attacked or pursued, it ejects into the water ; thus 

 completely blinding its adversary and effectually 

 covering its retreat. It is from this fluid that the 

 colour sepia is made. Besides carrying an ink- 

 bottle, some species of cuttle-fish are provided with 

 a long, delicate, horny pen, which forms a sort of 

 stiffener to the back. In some species the pen is 

 hard, thick, and broad, and the cuttle-fish bone of 

 commerce is a pen of this kind. The species found 

 in our waters is very small, and not at all 

 dangerous, being barely large enough to draw blood 

 from the hand ; but in the tropical seas they are 

 very large, powerful, and dangerous. 



The cuttle-fish is the original of Victor Hugo's 

 devil-fish, so vividly described in the " Toilers of 

 the Sea." If the devil-fish were a beneficent crea- 

 tion, I should be sorry to destroy your faith in it ; 

 but as it is, I believe it will be rather a relief than 

 otherwise 1o inow that in some important respects 

 Victor Hugo's story of it is a fable. The kraken 

 was a mythical cuttle-fish of fabulous size. — The 

 Amer' ... Ju':,aUst. 



' ■ 11^ \d. — There is every prospect of the 

 " Death'.} Head Moth" being very plentiful next 

 year. Severa 1 o" the "caterpillars" have been 

 caught in this locality. I have two in my posses- 

 sion. — Joseph Robinson, Chester •■le-Street. 



SEASIDE DIATOMS. 



AMONGST the " common objects " of the sea- 

 shore, Diatomace?e are perhaps the most 

 frequent, and the tyro in microscopic studies 

 generally desires to add a few of these beautifu 

 forms to his cabinet of slides. I am often asked, 

 How am I to procure them ? and when obtained, 

 How shall I prepare them ? I propose, with the 

 editor's permission, to answer both these queries ; 

 first premising that the inquirer has neither the 

 opportunity nor inclination to go on a dredging ex- 

 pedition, but to confine his search to the shore and the 

 brackish water-ponds in its neighbourhood. If he is 

 residing near a sandy and shelving shore, where the 

 receding tide leaves a large expanse of sand exposed, 

 he will be able to obtain most of the beautiful sand 

 species described by Dr. Donkin in papers on those 

 forms. His plan for procuring them is very simple 

 and very successful : the collector must provide 

 himself with a few 4-ounce bottles and a teaspoon, 

 and on the first sunshiny day, when the tide is at 

 the ebb, between the hours of 10 a.m. and 4 p.m., 

 he will betake himself to the beach, and as he ap- 

 proaches the receding waters he will observe the 

 sand-ripples and small depressions covered with a 

 yellowish-green film : this film consists almost wholly 

 of diatoms. Having previously partly filled one of 

 his bottles with sea-water at the nearest tide-pool, 

 he must carefully remove the film with the spoon, 

 and place it in the bottle ; shake it violently three 

 or four times, and he will observe the sand fall 

 rapidly to the bottom, leaving the diatoms floating 

 on the water : these he must quickly decant into 

 another bottle. By repeating this process he will 

 obtain copious, and frequently very clean gatherings. 

 On returning home, an examination of the living 

 frustules will repay the observer. He will probably 

 find Bacillaria cursoria crossing the field in various 

 directions, or have a Navicula sailing slowly about 

 their cell-contents rendering them conspicuous 

 objects. The first thought of the young observer 

 will be, Can these active little bodies be only plants ? 

 The second will be, By what means do they sail 

 about, apparently in search of food ? To the first 

 question I answer that a further study of plant-life 

 will satisfy him that the balance of probabilities is 

 in favour of their vegetable nature. To the second 

 I can only reply that our most acute observers are 

 unable to discover any organs of locomotion. 



We will now suppose our tyro has finished his 

 observations of the living frustule, and is desirous 

 of seeing the beautiful markings on the flinty shells 

 of these mysterious organisms. In order to do so 

 successfully, it is necessary to get rid of the internal 

 colouring matter (endochrome), and to separate the 

 two valves. All diatoms consist of two similar 

 (with few exceptions) silicious plates connected by 

 a less firmly silicious band : a pill-box, in which the 



