224 



EARTU-WORMS. 



E 



Month. 



Pharynx. 



EARTH-WORMS. The important part 

 played by earth-worms in the formation of 

 vegetable mold has been made the subject of a 

 special memoir by Charles Darwin. These ar- 

 ticulates are distributed all over the world, 

 being found io the loneliest islands of the sea, 

 even in Kerguelen Land. There are but few 

 genera of earth-worms, and they closely resem- 

 ble each other. Lumbricu* is the name of the 

 best-known genus. The species have not been 

 accurately distinguished and numbered; but 

 only a part of them bring up earth in the form 

 of castings, and are engaged in making tillable 

 soil. They appear to be found wherever there 

 is moist earth containing vegetable matter, but 

 seem to abound most where the ground is loose 

 and well charged with humus. Dryness is unfa- 

 vorable and even fatal to them ; but, although 

 they are terrestrial ani- 

 mals, they have been 

 found by M. Perrier to 

 be capable of living for 

 a considerable time un- 

 der water. During the 

 summer, when the 

 ground is dry, and dur- 

 ing the winter, when it is 

 frozen, they penetrate 

 to a considerable depth 

 in the earth and cease 

 to work. They are noc- 

 turnal in their habits, 

 and may often be seen 

 at night, crawling over 

 the ground, more often 

 moving their heads and 

 bodies around while 

 their tails are still in- 

 serted in their burrows. 

 Only sickly worms, 

 such as are afflicted by 

 the parasitic larva of 

 a fly, as a rule travel 

 in the day-time ; and 

 those which are seen 

 dead on the ground 

 after heavy rains are 

 supposed to have been 

 creatures afflicted in 

 some way that have 

 died of weakness rath- 

 Fio. l. DIAGRAM op THE er than by drowning. 



Z?SS2BrSfL. The bod 7 f f lar e e 



ftririM), (copied from Ray w orm consists ot one or 

 Lankester in " Quarterly two hundred almost 



SdXWo'KE nets'! cylindrical rings or seg- 



rk-s, pi. vii). ments, each furnished 



with minute bristles, 



and is endowed with a well-developed muscu- 

 lar system. The mouth is provided with a little 

 projection or lip, capable of taking hold of 



Calclferous glands. 



(Esophagus. 



Crop. 



Gizzard. 



Upper part of in- 

 tottta . 



things, and of sucking. Internally, a strong 

 pharynx, corresponding, according to Perrkr, 

 with the protrusile trunk or proboscis of other- 

 annelids, and which is pushed forward when 

 the animal eats, is situated behind the mouth. 

 The pharynx leads into the oesophagus, on each 

 side of the lower part of which are three pairs 

 of large glands, which secrete a surprising 

 amount of carbonate of lime. They are unlike 

 anything that is known in any other animal, 

 and their use is largely a matter of speculation. 

 They are probably partly excretions of the ex- 

 cess of lime contained in the leaves which the 

 animal eats, and may otherwise aid digestion 

 by affording a neutralizing agent against the 

 acids of its food. In most of the species the 

 oesophagus is enlarged into a cup in front of 

 the gizzard. The latter organ is lined with a 

 smooth, thick, chitinous membrane, and is sur- 

 rounded by weak longitudinal but powerful 

 transverse muscles. Grains of sand and small 

 stones, from one twentieth to a little more than 

 one tenth of an inch in diameter, may be found 

 in the gizzard and intestines, and are supposed 

 to serve, like millstones, to triturate the food. 

 The gizzard opens into the intestine, -which 

 presents a peculiar remarkable longitudinal 

 involution of the walls, by which an extensive 

 absorbent surface is gained. The circulatory 

 system is well developed. Breathing is per- 

 formed through the skin, without special re- 

 spiratory organs. The nervous system is fairly 

 developed, with two almost confluent cerebral 

 ganglia situated near the anterior end. 



Worms have no eyes, and are measurably 

 indifferent to light; yet they can distinguish 

 night from day, and are quickly affected by a 

 strong light, and after some time by a moder- 

 ate light shining continuously upon them. They 

 do not much mind a moderate radiant heat, 

 but are sensitive to cold. They have no sense 

 of hearing, but are extremely sensitive to vi- 

 brations in any solid object. Worms in pots, 

 which had paid no attention to the sound of a 

 piano, when placed on the piano instantly drew 

 into their holes when the notes were struck. 

 Their whole body is sensitive to contact, as of 

 a puff of air. Their sense of smell is feeble, 

 but responds fairly well to the odor of the cab- 

 bage and onion or whatever they like. They 

 are omnivorous, and swallow enormous quan- 

 tities of earth, out of which they extract any 

 digestible matter which it may contain ; they 

 also consume decayed and fresh leaves and veg- 

 etable matter, and raw, roasted, and decayed 

 meat, but like raw fat best. 



Mr. Darwin discovered in worms evidences 

 of a degree of intelligence. They line their 

 burrows with leaves as a protection, it is sup- 

 posed, against the cold of the clammy ground, 

 and plug the entrances to them with leaves 





