376 



HISTORY OF FISHES. 



of four or five yards. A spiral line of blue bead-like bo- 

 dies, Jess than the head of a pin, revolves around the 

 cable from end to end, and under the microscope these 

 beads appear covered with minute prickles, so hard and 

 sharp, that they will readily enter the substance of wood, 

 adhering with such pertinacity that the cord can rarely 

 be detached without breaking. It is to these prickles 

 that the man-of-war owes its power of destroying animals 

 much its superior in strength and activity. When any 

 thing becomes impaled upon the cord the contractile 

 fibres are called into action, and rapidly shrink from 

 many feet in length to less than the same number of 

 inches, bringing the prey within reach of the little tubes 

 by one of which it is immediately swallowed. 



I might now proceed to describe many analogous ani- 

 mals scarcely inferior in interest, but it is time to notice 

 some individuals of another tribe, residing beneath the 

 surface, and therefore less generally known. 



The grandest of these is the beroe. In size and form 

 it precisely resembles a purse, the mouth, or orifice, an- 

 swering to one of the modern metallic clasps. It is per- 

 fectly transparent ; and in order to distinguish its filmy 

 outlines, it is necessary to place it in a tumbler of brine 

 held between the observer and the light. In certain di- 

 rections the whole body appears faintly irridescent, but 

 there are several longitudinal narrow lines which reflect 

 the full rich tints of the rainbow in the most vivid man- 

 ner, for ever varying and mingling the hues, even while 

 the animal remains at rest. Under the microscope these 

 lines display a succession of innumerable coloured scales 

 or minute fins, which are kept unceasingly in motion, 

 thus producing the play of colours by continually chang- 

 ing the angle of reflection. The movements of the beroe 

 are generally retrograde, and are not aided by the col- 

 oured scales, but depend upon the alternate contraction 

 and dilatation of the mouth. The lips are never per- 

 fectly closed, and the little fish and shrimps which play 

 around them are continually entering and leaving them 

 at pleasure. The animal is dependent for its food upon 

 such semi-animated substances as it draws within its 

 grasp by moving slowly backwards in the water, and 

 retains them in consequence of their own feebleness and 

 inability to escape the weakest of snares. 



Another tribe of the sea-purses (Salpa), though much 

 smaller than the beroe, are more complex in structure, 

 and possesses a higher interest in consequence of the sin- 

 gular habits of some of the species. They are double 

 sacks, resembling the beroe in general form, but desti- 

 tute of irridescence. The outer sack, or mantle, rarely 



exceeds an inch in length, and is commonly about half 

 as wide. The inner sack is much smaller, and the in- 

 terval between these forms a cavity for the water which 

 they breathe, and for some of the viscera. Their visible 

 organs are a transparent heart, which can only be seen 

 in the strongest light ; a splendid double row of whitish 

 bead-like cavities forming a spiral line near one extrem- 

 ity, and supposed to be either lungs or ovaries ; numerous 

 broad, fiat, pearly muscles, barely distinguished by their 

 mistiness, and an alimentary canal as fine as horse-hair, 

 with a slight enlargement at one spot, which has been 

 called a stomach. This enlargement resembles both in 

 size and colour a grain of sand. From the base of the 

 animal arises two longer and four or five shorter conical 

 spines of jelly, curved into hooks at the points, by means 

 of which numerous individuals attach themselves toge- 

 ther in double rows like the leaflets of a pinnated leaf. 

 Cords of this kind, composed of forty or fifty animals, 

 were often taken, but they separate and reattach them- 

 selves at pleasure. 



To the gregarious habits of this little mollusque we 

 owe a very singular and striking phenomena, which I 

 have never seen noticed by naturalists, although we fre- 

 quently witnessed it near the Cape of Good Hope. The 

 animals are occasionally found associated together in such 

 countless myriads that the sea is literally filled with them, 

 sometimes over three or four square miles of surface, 

 and to the depth of several fathoms. The yellow spots 

 which have been described being the only coloured por- 

 tions of their body, give to the whole tract the appear- 

 ance of a shoal or sand-bank at some distance below the 

 surface. The deception is heightened by the greater 

 smoothness of the water at these places, particularly in 

 calm weather ; for so closely are the animals crowded to- 

 gether, that the water is rendered in a manner less fluid , 

 the smaller billows break around the margin and are lost, 

 while the heavy waves of the Southern ocean are some- 

 what opposed in their progress, and take on in a slight 

 degree the usual appearance of the ground-swell. There 

 can be but little doubt that many of the numerous shoals 

 laid down in the charts of this region, but which have 

 never been seen by any but the supposed discoverers, 

 have been immense banks of these gregarious mollusc-se. 

 In sailing through a tract of this description, in which the 

 progress of the ship was very sensibly retarded, I have 

 dipt up with the ship's bucket a greater bulk of the ani- 

 mals than of the water in which they were suspended. 

 How wonderful are the effects produced by the minute 

 links of creation !" Dr Reynall Coates of Philadelphia. 



