114 TKANSACTIONS OF THE ILLINOIS 



If we watch the process of growth in our little egg we shall see the 

 yolk-surrounding fluid first gathering into a denser ring, while that 

 on the inner side is breaking up into granules (shown on diagram), as 

 the first step towards forming cells, out of which the tissues are to be 

 made. As the process goes on the surrounding ring becomes more dis- 

 tinct and is marked externally with prominences and strictures, until at 

 length distinct segments are formed and the little caterpillar is clearly 

 outlined. 



The position the caterpillar occupies in the egg is quite different 

 from that in the more flattened and disk-shaped eggs (diagram referred 

 to); the head is also brought opposite the point of least resistance to an 

 inside force. After eating its way out of its prison, the first act of the 

 caterpillar, as long ago observed in reference to its congener, P. brassiccs, 

 by Harold, is to eat the shell ; a habit which appears to be followed by 

 most, if not all, of the species of the genus. 



Although the caterpillar, when it has attained its growth, is painted 

 with the most delicate emerald tint, and trimmed with a dorsal line and 

 lateral dots of gold, its beauty has but little attraction for the gardener, 

 nor can he take any pleasure in watching it as it riddles the leaves of his 

 cabbages with holes and bores its way into the forming heads. Though of 

 a rqmarkably quiet and peaceable disposition, not venturing to encroach 

 in the least upon the rights of other insects, passing carefully around even 

 the little plant-louse rather than disturb it, the gardener, regardless of this, 

 declares a war of extermination; and to this end salts it, brines it, limes 

 it, powders it with hellebore, soot, ashes, tobacco, pepper, etc. ; drenches 

 it with hot water, soap-suds, lye, elder-juice, decoction of dog-fennel, 

 dilute carbolic acid and a host of other obnoxious things; and, finally, 

 saves some of the most promising heads by picking the worms off of 

 them. 



How are we to explain the remarkable tenacity of life in a worm 

 apparently so extremely delicate and tender? Not only will many 

 survive the treatment described, but may often be observed feeding away 

 when coated over with lime, hellebore, etc. They have even been 

 frozen in ice, and yet, when thawed out, lived and completed their 

 transformations. Why is it that a substance which destroys the currant- 

 worm has no injurious effect upon them? Will you answer, that it is 

 some peculiarity of their nature? But what is this peculiarity? The 

 tissues of their bodies are apparently as delicate as those of the saw-fly 

 larvae. 



And here we may call attention to the fact that although the cater- 

 pillar is so peaceable and unaggressive, on the other hand the perfect 

 insect or butterfly is of an exactly opposite disposition. While other 

 allied species, with the exception of P. brassicce, are more or less confined 

 to their faunal regions, this one not only ranges over Europe, from Lap- 

 land to the Mediterranean Sea, and over Asia from Siberia to the tropics 

 and eastward to China, but has crossed the Atlantic and traversed 

 North America from the eastern shore to the Missouri, driving before it, 

 or out of the pathway of its progress, our native species. When it 



