S2 



HA RD WICKE* S SCIENCE- G OSSIP. 



a long and extensive period of study, Swammerdam, 

 who wrote the " Book of Nature," is almost the only 

 observer who has devoted any attention to the sys- 

 tematic study of these eggs ; but the result of his 

 researches was such that he writes: "Among all 

 the eggs of insects, of which I have various species in 

 my collection, I know none more worthy of greater 

 attention than these." 



It will perhaps be thought that I have tried the 

 patience of the reader sufficiently, and ought now to 

 drop my parable, and state the name of the animal 

 which owns this wonderful egg. A few years ago I 

 should not have dared to name the despised earth- 

 worm. To let the public of twenty years ago know 

 that you condescended to notice the worms of earth 

 would be to signify your fitness for the asylum, but 

 Darwin has changed all that, and now we are told by 

 the author of "In Darkest England" that "more 

 minute, patient, intelligent observation has been 

 devoted to the study of earthworms, than to the 

 evolution, or rather degradation, of the sunken section 

 of our people." Each subject has its place, and we 

 have no more right to ignore the one than the other. 

 If we were by some calamity to lose this lowly 

 population of mead and woodland, our beautiful, 

 fertile land would in a single year depreciate in 

 value to the extent of millions of pounds ! Hence I 

 am bold enough to mention the earthworm as the 

 creature whose egg is a microcosm of the greatest 

 wonder. The case which contains the fluid-matter 

 out of which the future worm is to be evolved is of a 

 horny, not of a calcareous substance. It reminds us 

 of the egg- capsules of the dog-fish found everywhere 

 on the sea-coast. Chemically it corresponds almost 

 exactly with our nails, and with the hoofs and 

 horns of animals. It is cuticular in origin, that is, 

 the skin, and not the blood, the spleen, or any 

 other internal organ or substance is the agent in its 

 formation. 



Everyone knows that the finger-nails are most 

 easily trimmed after the hands have been washed in 

 warm water. The reason is plain. Horny sub- 

 stances absorb moisture, and swell in proportion to 

 the amount taken up, at the same time becoming 

 soft and pliable. Slight chemical changes produce 

 greater or lesser degrees of hardness in the substance. 

 Hence horny substances are not all alike hard, and 

 the horny-capsule of the worm is tolerably elastic, so 

 that when kept in a moist condition it can be slightly 

 expanded by the internal pressure exerted by the 

 growing worm. But how can the worm grow ? The 

 chick can become no larger than the shell-surrounded 

 yolk and albumen will permit, but when the young 

 worm is hatched it will very probably be an inch in 

 length. Let us see how this contingency is provided 

 for. The accompanying illustration will help to 

 make the matter plain. If we took a small tube of 

 gelatine, and placed within its cavity a tiny globule, 

 we could secure the contents of the tube by drawing 



the two ends to a point. If now the globule could 

 expand on the application of moisture it must either 

 burst its case, cause it to expand in the direction of 

 its shortest diameter, or force open the ends of the 

 tube. Now the egg-capsule of the worm can expand 

 slightly, but not to a sufficient extent to allow the 

 worm to reach full dimensions. Consequently the 

 embryo gradually forces open the sealed extremity of 

 the case, and thus paves the way for its ultimate- 

 escape, at the same time that it loosens its swaddling 

 bands, and develops little by little into a perfect 

 worm. While the beak of the embryo bird develops 

 and hardens within the shell sufficiently to enable i; 

 to peck its way out of the calcareous covering, the 

 worm has no such tool for opening its prison-house, 

 and so these other means must be provided for its- 

 escape. 



It may occur to some observant reader that analogy 

 to this is found' in the case of the dung-flies' eggi>, 

 which are deposited with the horn-like projections 

 upwards. In both cases if the eggs are removed 

 from their moist lodging-place they shrivel and be- 

 come lifeless. Worms again are not quite alone in 

 the possession of the power to extend the egg-case 

 during incubatiou. Huber long ago observed the 

 same fact in relation to the eggs of ants, and those of 

 certain saw-flies can similarly expand to meet the 

 requirement of the growing grub within. 



As the larvae of various caterpillars are subject to 

 the attacks of sundry deadly parasites, so I have 

 found (what does not appear to have been observed 

 before), that the eggs of worms are often rendered 

 abortive by the invasion of a smaller worm. It is 

 another illustration of the rhyme about "big fleas 

 and little fleas." Whether the eggs of the parasite, 

 which often exist in great numbers in the adult 

 worm, pass with the ovule of the true worm into the 

 capsule and then develop, living on the matter stored 

 up in the egg-case, or whether the parasite finds its 

 way into the egg after oviposition has taken place, is 

 uncertain, but I believe the former suggestion to be 

 the correct one. 



It would occupy too much space, and to some 

 readers at least prove uninteresting, if I were to- 

 detail the wonderful process which goes on within 

 the egg-case. The life-history of the worm has been 

 fully studied, and is replete with marvels. If an 

 egg is examined when the young embryo is almost 

 ready to emerge, it will be possible, through the 

 semi-transparent and greatly-dilated case, to watch 

 the movements of the worm, trace the current of 

 blood along the elaborate system of vessels, and 

 eventually observe the emergence of the baby annelid 

 into the world. 



There is much food for reflection in this curious 

 egg, and now that I have preached my sermon I 

 leave my readers to decide whether accident or design 

 will best account for the adaptation of this insigni- 

 ficant germ to its environment and uses. 



