3Q 



SCIENTIFIC NEWS. 



[July 13, iJ 



THE NATURALIST AT THE SEA-SIDE. 



1. — The Tow Net. 



ON a fine sunny day the naturalist at the sea-side can 

 get many treasures by working a tow-net. This 

 is a long tapering bag, from three to five feet long, made 

 of stout and fine muslin. The open end is sewn to an 

 iron hoop from six inches to a foot in diameter. The 

 other end is open, but fitted with tape so that it may 

 either be tied up or have a glass tube inserted. The 

 hoop is held by means of three cords knotted into one. 

 For special purposes one side of the hoop may be 

 weighted, and the opposite side buoyed up with cork, 

 but the tow-net should never be made so light as to float. 

 When the net has been plied on the surface of the sea 

 for half an hour, it is turned inside out into a clear vessel 

 of sea-water. The captured animals float out and are 

 either examined on the spot, or preserved for future 

 study. Glass dipping-tubes of different sizes are needed 

 to pick up small objects, and "concentrators" are useful 

 for getting rid of the great mass of superfluous water. 

 The concentrator is a lacquered cylindrical tube, made of 

 fine gauze above, but capable of holding a small quantity 

 of water below. If a gallon of water be poured through 

 it all the visible organisms which it contains will be 

 strained out into an ounce or two of fluid in the bottom 

 of the tube. In working the net, a rowing-boat, or any- 

 thing that moves on the sea, can be used, provided that 

 it does not go too fast. A speed of two or three miles an 

 hour is suitable. 



So much for the tackle and mode of working. We 

 will now suppose that our naturalist is at sea. Since it is 

 just as easy to wish him good luck as bad, we will further 

 suppose that he has a bright day and still water. If he 

 is in a small boat he should have two or three wide jars 

 at his feet, each to serve for a separate haul. If he be in 

 a large craft and out for the day he must further be pro- 

 vided with a portable microscope, collecting tubes, and a 

 supply of preservative fluid. 



The things that he will find depend upon season and 

 locality. To name all the likely things would be to 

 empty a zoological text-book upon our readers. Let us 

 be moderate then and notice only three kinds of animals, 

 which are commonly met with and well worth study. 

 The tow-net is pretty sure to bring up (1) small swim- 

 ming Crustacea, microscopic shrimps we might call them; 

 (2) medusoids, and (3) echinoderm larvae. 



The surface crustacea will afford endless occupation 

 in the determination of species, but this is work for the 

 specialist. It will be enough for the beginner if he can 

 recognise two orders which are sure to be met with, 

 leaving details to others. The orders in question are 

 the amphipods and the copepods. The amphipods are 

 generally flattened from side to side, and provided with 

 a crowd of legs beneath. At the tail-end a^e three 

 pairs of tail-fins, which are used to make a sudden leap 

 in the water. The legs next in front are very small. 

 The copepods may be recognised with a pocket-lens as 

 small, many-jointed crustacea, having four or five 

 branched swimming legs on the fore part of the abdo- 

 men, and behind these a five-jointed tapering tail, 

 without appendages. Far more interesting than these 

 to the young biologist are the many larval crustacea 

 which swim on the top of the summer sea. Look up, 

 for instance, in any good manual of zoology, the larval 

 form known as a Nanplius. The nauplius is an ances- 

 tral crustacean type, which was no doubt in its day an 



adult stage. In these later ages of the world's history 

 it is usually a transitory phase of crustacean life, gene- 

 rally turning into something else, and ending up as a 

 barnacle, a copepod, or a shapeless parasite. The zoaja, 

 or larval stage of many crabs, is another and more ad- 

 vanced embryo, whose form should be studied before- 

 hand. There is a world of interesting speculation 

 opened out by these crustacean larvae. Anyone who 

 has examined under a microscope a nauplius and a 

 zoaea in a watch-glass of sea-water will know what to 

 make of those discussions of Darwin, and Haeckel, and 

 Fritz Miiller which seem so hard and dry to those who 

 seek to master zoology by mere reading and thinking. 



The tow-net often brings up medusoids, which at first 

 sight look like brown or red spots entangled in a clear 

 jelly. Give them plenty of water to swim in, and watch 

 them under the microscope until you can make out the 

 eye-spots and the tentacles, and the polyp hanging down 

 in the middle of the transparent bell. These medusoids 

 are detached from tree-like colonies, and will in turn 

 produce such colonies again. 



If your curiosity is capable of being roused by strange 

 transformations you will find echinoderm larvae very 

 fascinating. The Bipinnaria of the star-fish, and the 

 Pluteus of the echinus "or sand-star are common forms. 

 Utterly unlike the adult animals, into which they are 

 transformed, these larvae are well adapted for locomotion. 

 They have long arms, ciliated bands, and a delicate 

 skeleton of calcareous spicules. Elaborate figures would 

 be needed to give even a rough notion of their various 

 shapes. Sometimes the rudiment of the permanent 

 body may be seen budding out from the larva. 



The zoologist who has become familiar with the crusta- 

 cean, hydrozoan, and echinoderm larvae may exercise his 

 thoughts profitably upon the great number of marine 

 animals which develop with conspicuous metamorphosis. 

 It is quite otherwise with animals of high grade, and 

 with all the inhabitants of land and fresh waters. These, 

 as a rule, develop directly. In the waters of the sea 

 locomotion is very easy and advantageous, and at the 

 same time enemies abound. These conditions favour the 

 production of a vast brood of tiny embryos, which disperse 

 at once in search of food, and only attain the adult con- 

 dition by an entire change of structure and mode of life. 

 In fresh waters, on the other hand, locomotion is limited 

 by the small size of the area, while life is a less difficult 

 struggle than in the sea. Fewer embryos are produced, 

 and these are cared for by their parents, if only to the 

 extent of having a good supply of food-yolk laid up for 

 them in the egg. They hatch out in a comparatively 

 advanced condition, resembling the parent, except in size. 

 Terrestrial conditions are unfavourable to metamorphosis, 

 owing to the difficulty which the immature animal finds 

 in moving about on dry land. Lastly, all big and strong 

 animals of high intelligence find it best to bring up a few 

 young at a time, and to feed and protect these few until 

 their development is far advanced. 



We must add a few words about preservatives. Picric 

 and chromic acid solutions are of great use in special 

 cases, and have the merit of being extremely cheap. The 

 picric acid solution should be saturated, the chromic acid 

 one quarter per cent. For general purposes nothing is 

 better than Haentsche's fluid, viz., a mixture of glycerine 

 (two parts), methylated alcohol (one part), and distilled 

 water (one part). After placing in the fluid, sort out the 

 organisms by means of a dipping tube into little bottles, 

 and be careful to label each with time and place of capture. 



