Apbtl ], 1865.] 



SCIENCE-GOSSIP. 



75 



long tortuous tubes, are attached to them in front, 

 and six well-formed biliary canals, which represent 

 the liver, are connected with them behind. Opening 

 into the mouth and the spinning apparatus which we 

 alkided to before, may be seen two pecuHar organs, 

 which extend in a tortuous manner along the entire 

 length of the stomach, and whose office is the secre- 

 tion of the fluid from which the silk is formed. 

 Every portion of this digestive apparatus is cal- 

 culated to extract the nutritious materials from the 

 crude masses of unsubstantial food which has been 

 imperfectly prepared by the action of the jaws. 



Even on the second day after the caterpillar has 

 been converted into the chrysalis, very considerable 

 alterations may be observed. The oesophagus is 

 narrowed and elongated; the intestine, similarly 

 modified, is now divided into two well-marked 

 regions ; the stomach has been diminished by about 

 one-half of its breadth and a quarter of its length ; 

 the salivary and biliary glands have been shortened, 

 and the organs which secrete the silk have become 

 smaller. On the eighth day, the entire digestive tube 

 is exactly like a spindle one-half of which is covered 

 with thread, and which is loaded with lead in order 

 to balance it. The oesophagus represents the upper 

 portion of the spindle ; the stomach corresponds 

 to the middle, which is covered with thread ; tlie 

 small intestine to the thin portion, and the large in- 

 testine to the loaded part. At the sam.e period the 

 salivary glands and biliary coeca are reduced by about 

 two-thirds, and the silk-secreting organs appear as 

 two very slender threads. 



Durmg the entire winter — that is to say, for five 

 or six months of the year — these operations are sus- 

 pended ; but they are recommenced in fine weather, 

 and continued till the insect is fully formed. In a 

 short time the silk-forming canals have entirely dis- 

 appeared ; hardly a trace of the salivary glands is to 

 be found ; and the stomach, though preserving its 

 former shape, has decreased in size ; but to compen- 

 sate for this, it has developed a new cavity called 

 the crop, which is destined to assist in sucking up 

 the juices of the flowers, and retaining them till re- 

 quired by the insect. Moreover, the two intestinal 

 regions have become more distinct, and the large in- 

 testine has developed an accessory pouch, not a 

 trace of which existed hitherto. 



We come now to the nervous system. In insects 

 in every condition, this system is composed of two 

 distinct portions. The brain is placed in the head 

 just above the oesophagus. The other nervous 

 masses, or ganglia, are situate below the digestive 

 tube, where they constitute a ganglionic chain. The 

 brain is united to the first ganglion, this to the 

 second, and so on, by a series of nervous filaments, 

 technically termed commissures. In each ring of 

 the caterpillar's body there is a distinct ganglion ; 

 consequently there are in all twelve of these struc- 



tures, equally distant from each other, with the ex- 

 ception of the two first, which are more closely 

 approximated than the rest. The brain itself is 

 very small, and is composed of two smooth lobes 

 which are obliquely united, and give off a few slender 

 nervous filaments. 



Two days after the caterpillar has been converted 

 into the chrysalis, the ganglionic chain has been 

 shortened one-fourth, and various changes of altera- 

 tion and concentration have begun. Some ganglia 

 are approximated; others, on the contrary, are sepa- 

 rated. At about the eighth day the chain has been 

 shortened one-half. On the fourteenth the brain 

 and first ganglion have come so close together that 

 their commissures surround the oesophagus ; the 

 fourth and fifth ganglia have been fused together ; 

 and the sixth and seventh are hardly perceptible. 

 Nov.r there is a period of rest, brought about by the 

 approach of winter. Then, after the latter season, 

 the operations are recommenced, and when they are 

 again arrested, after the last apparent transforma- 

 tion, there are only eight ganglia to be seen. The 

 second, third, fourth, and fifth, have given rise, by 

 their fusion, to two large masses, which are placed 

 in the chest quite close to each other ; the sixth and 

 seventh have completely disappeared, and their 

 former position is alone marked by the origin of a 

 few nervous filaments ; the five posterior ones have 

 undergone little or no change. Finally, the brain 

 itself had become twice as large, its lobes have as- 

 sumed a transverse position, and each of them gives 

 origiu to a large optic nerve which travels to one of 

 the compound eyes. 



The changes which the organs of circulation and 

 respiration undergo are not by any means as well 

 known as those we have been describing, and this 

 ignorance is due, most likely, to the great simplicity 

 of the first, and the equally complex character of 

 the second. In this caterpillar, as in every other 

 one, the circulation is almost entirely lacunar. In 

 it, as in the butterfly, there is a distinct heart, or 

 rather its representation, in the form of a long 

 many-chambered canal, stretching from end to end 

 of the body. When the latter is shortened, this 

 dorsal vessel, as it is called, is also diminished in 

 length, and becomes more and more tortuous in 

 proportion as the regions of the body are mapped 

 out and separated from each other. 



This degradation of the circulatory organ is 

 compensated for by the formation and distribution 

 of a series of respiratory organs, or trachefe. These 

 open externally at the stigmata to which we have 

 alluded already. They consist, in Pieris, as in all 

 other caterpillars, of two great lateral trunks, 

 reaching from end to end of the body, and giving 

 off hundreds of branches and ramifications, which 

 travel over the whole frame, penetrate the smallest 

 cavities, and supply the most delicate organs. In 



