The openings at the end of the breathing tubes, on the surface of the insect's body, are known, as we have said, as 'spiracles,' or 'stigmata.' They can be closed at will by special muscles, and, to prevent dust from getting into the tube, the rim of each spiracle has a more or less complicated fringe or strainer. In fig. 3 the spiracle is shown open, the opening being marked by the letter O. When closed the fringes interlock like clasped fingers.

Fig. 1 shows the position of the breathing tubes in the aphis or green fly. The spiracles or pores are marked O, the breathing tubes T.

Some insects which live in water, such as the water-beetle, breathe air in the same way as their relatives who live on land. To do this they have to come frequently to the surface of the water to take in fresh supplies of air. In the great Dyticus water-beetle this is done in a curious way. The creature, rising to the surface, first thrusts its tail up into the air, and then bending it downwards, lets the air rush in to fill the s.p.a.ce between the body and the upper wing-cases. This done, the tail is pressed back again, and the beetle returns to the depths, where the imprisoned air is taken in through the pores into the tubes.

Besides the system of tubes just described, many insects possess a wonderful system of air-cells, which give extra help in breathing during flight. These air-cells are largest in insects which fly most. It is a curious fact that birds have an exactly similar system; in many cases, even the bones of birds are filled with air. It is generally stated, indeed, that birds with the strongest flight have the most 'pneumatic'

bones. This not quite true, for the swallow, for example, has the long bones of its wing filled with marrow, and not with air. Other birds, however, like the storks, which fly much, and the owls and nightjars, have all the bones in the body thus filled with air which they obtain from the air-cells.

W. P. PYCRAFT, F.Z.S., A.L.S.

AFLOAT ON THE DOGGER BANK.

A Story of Adventure on the North Sea and in China.

(_Continued from page 227._)

CHAPTER V.

'I shall not be able to make plum duff,' said Charlie to Ping w.a.n.g, about half an hour after his loss of the cook's recipe-book.

'There will be a row if the men discover that you don't know how to make it,' Ping w.a.n.g declared, looking serious. 'But never mind that, I have something more important to tell you. Come aft; the skipper may be listening to what we are saying.'

They went right to the stem of the trawler and stood against the gunwale.

'No one can come near us without our seeing him,' Ping w.a.n.g said, and continued at once: 'Could you swim a mile in a sea like this?'

'I think so.'

'Then let us desert the _Sparrow-hawk_ when darkness comes on.'

'But where are we to swim to? I don't see any boats within five miles of us.'

Ping w.a.n.g pointed to the horizon, where the smoke of about half-a-dozen trawlers was plainly visible.

'That's a fleet of steam trawlers,' he declared, 'and before midnight we shall be among them. When one comes within a mile or so of us, we will jump overboard and swim to her. The skippers and men on the steam trawlers belonging to the large fleets are splendid fellows, and when they hear what a beast Skipper Drummond is, they won't send us back. We must start as soon as possible after the midnight shoot, if there is any trawler near us then.'

'Suppose the skipper thinks we have fallen overboard and sends a boat to rescue us?'

'I don't think that he would take the trouble. But listen! I can hear him on the bridge. Don't let him see us talking, in case he suspects that we are up to something.'

Ping w.a.n.g made his way for'ard, while Charlie returned to the galley and busied himself in making buns. He had made some on the previous evening, and although he did not enjoy the one that he tasted, the crew found no fault with them.

As he worked, he could see through the porthole that the fishing fleet was drawing nearer. Some of the trawlers were miles away on the starboard bow, and others on the port.

Three hours later, when it was dark, Charlie counted twenty-five trawlers, and every now and again he could see the mark-ship's rockets piercing the night gloom. At ten o'clock he calculated that the nearest trawler was quite three miles away, and judging from the course the steamers were taking, he began to fear that it would come no nearer. But shortly before the men turned out to haul, Ping w.a.n.g popped his head into the galley and beckoned Charlie to come outside.

'As soon as we have hauled and shot,' he said in a whisper, 'we must slip off aft and dive overboard.'

'We shall have to swim nearly two miles.'

'Oh, no; nothing like that distance,' Ping w.a.n.g declared, and pointed to a smack on the starboard side which Charlie had not noticed.

'It's a mission ship,' Ping w.a.n.g explained, 'and she will lay to until daybreak. By the time that we have hauled and shot we shall be abreast of her, and won't have more than half a mile to swim. The skipper is fast asleep, and, as the mate is not going to disturb him, we shall have a quiet haul.'

A few minutes later, Charlie and Ping w.a.n.g were tugging at the cold, dripping net, delighted at the thought that it was the last time they would have to perform such work.

'It's a splendid haul,' the bo's'un called out to the mate, as the net of fish was swung over the pound.

As he spoke, the fish fell with a splash in the pound, and, the catch being extra large, many of the bigger fish jumped out of the enclosure and wriggled and slid about the deck. Charlie and another man picked them up and tossed them back into the pound.

As soon as the net had been let right out again, Charlie walked aft and found that Ping w.a.n.g was already there. The other men had gone for'ard to clean and pack the fish.

'Are you ready?' Charlie asked.

'Quite,' Ping w.a.n.g answered, and at once they began to undress.

'I shall not take off my under-clothes,' Charlie said, 'in case the water is very cold.'

'Nor will I,' Ping w.a.n.g said.

In a few moments both were ready.

'Chinee!' the mate shouted from the bridge. 'Chinee!' the men in the fish-pound repeated.

'They have missed us,' Charlie said. 'I'm off.' He climbed on the starboard gunwale, balanced himself for a moment and then dived into the sea. Ping w.a.n.g was after him in an instant.

Charlie saw the sailing-boat and made towards it.

'Let us keep close together,' he said to Ping w.a.n.g, 'in case anything should happen to either of us.'

Ping w.a.n.g did not wish to waste his breath in talking, but showed that he agreed with Charlie's suggestion by drawing closer to him. For a time--they did not know for how long--they swam silently onwards, but there was a big ocean swell, and often the ship for which they were bound was completely hidden from their sight for some minutes. When they did catch sight of her, they found that they were not making rapid progress. They were still a long way from the ship, and when they had been swimming for a good time, Ping w.a.n.g's courage began to fail him.

'I shall never reach her,' he declared, 'I'm getting tired. It is all up with me.'

'Nonsense, man,' Charlie answered, swimming a little closer to him.

'Have a rest; float.'

Ping w.a.n.g acted on Charlie's advice.

'She was much farther from the _Sparrow-hawk_ than we thought,' Ping w.a.n.g declared, when he had rested for a few moments.

'You're right,' Charlie answered; 'but we shall reach her in ten minutes at the latest.'

Ping w.a.n.g, encouraged by what Charlie had said, turned over and resumed swimming.