436 THE POPULAR SCIENCE MONTHLY. 



there is a score or more of larger and shorter tubular organs, which are 

 called the pyloric caeca. These open into the intestine, and their aper- 

 tures may be seen on one side of it, occupying an oval space, in the 

 middle of which they are arranged three in a row. 



The chief food of the herring consists of minute Crustacea, some 

 of them allied to the shrimps and prawns, but the majority belong- 

 ing to the same division as the common Cyclops of our fresh waters. 

 These tenant many parts of the ocean in such prodigious masses that 

 the water is discolored by them for miles together, and every sweep of 

 a fine net brings up its tens of thousands. 



Everybody must have noticed the silvery air-bladder of the her- 

 ring, which lies immediately under the backbone, and stretches from 

 close to the head to very near the vent, being wide in the middle and 

 tapering off to each end. In its natural state, it is distended with air ; 

 and, if it is pricked, the elastic wall shrinks and drives the air out, as 

 as if it were an India-rubber ball. When the connections of this air- 

 bladder are fully explored, it turns out to be one of the most curious 

 parts of the organization of the whole animal. 



In the first place, the pointed end of the sac or crop into which 

 the gullet is continued runs back into a very slender duct which turns 

 upward and eventually opens into the middle of the air-bladder. The 

 canal of this duct is so very small and irregularly twisted, that, 

 even if the air-bladder is squeezed, the air does not escape into the 

 sac. But, if air is forced into the sac by means of a blowpipe, the air 

 passes without much difficulty the other way, and the air-bladder be- 

 comes fully distended. When the pressure is removed, however, the 

 air-bladder diminishes in size to a certain extent, showing that the air 

 escapes somewhere. And, if the blowing up of the air-bladder is per- 

 formed while the fish is under water, a fine stream of air-bubbles may 

 be seen to escape close to the vent. Careful anatomical investigation, 

 in fact, shows that the air-bladder does not really end at the point 

 where its silvery coat finishes, but that a delicate tube is continued 

 thence to the left side of the vent, and there ends by an opening of 

 its own. 



Now, the air-bladder of all fishes is, to begin with, an outgrowth 

 from the front part of the alimentary canal, and there are a great 

 many fishes in which, as in the herring, it remains throughout life in 

 permanent communication with the gullet. But it is rare to find the 

 duct so far back as in the herring ; and, at present, I am not aware 

 that the air-bladder opens externally in any fishes except the hemng 

 and a few of its allies. 



There is a general agreement among fishermen that herrings some- 

 times make a squeaking noise when they are first taken out of the 

 water. I have never heard this sound myself, but there is so much 

 concurrent testimony to the fact that I do not doubt it ; and it occurs 

 to me that it may be produced, when the herrings are quickly brought 



