NATURAL SCIENCES OF PHILADELPHIA. 51 



mon tenements for hundreds of individuals of particular species. 

 This is the case with our common American Fruit Caterpillar, 

 Clisiocampa Americana. 



It has been said that the Caddice worms construct cases in which 

 they reside, and which they close by means of threads at the ends 

 when about to pupate, so as to admit the water through their in- 

 terstices, and keep out enemies. It is obvious that water does 

 not injure the pupa?. Nature, like a faithful nurse, carefully pro- 

 tects the interests of every one of her countless progeny by making 

 its inner life correspond with outer actions. On the ground that 

 water is beneficial to the pupa of a Phryganea, we have an expla- 

 nation of the comparative openness of its cocoon at the ends. 



It was further remarked that Paraponyxin the larval condition 

 was endowed with both branchiae and spiracles. This seems to 

 be a very wise provision of nature. The branchiae enable the in- 

 sect to breathe like fishes, when immersed in a watery element. 

 May it not be that the spiracles are quiescent, and only come into 

 possession of their legitimate function when the chiysalis state 

 has been assumed, and the animal is inclosed in a cocoon which 

 is perfectly tight ? As the chrysalis while in this stage respires 

 but feebly and imperceptibly, there is in this home of its con- 

 struction, an ample capacity of air for the accommodation of its 

 wants. 



It is affirmed that Lepidosiren, in addition to lungs, possesses 

 both internal and external gills ; the latter being in a rudimentary 

 condition in the adult form. The rivers of South America and of 

 the east and west shores of Africa, where this animal exists, during 

 drouth are dried up. Did it breathe entirely by means of gills, 

 it would be in danger of extinction during the dry season ; but 

 being endowed with lungs also, it is enabled to meet the con- 

 tingency, and thus survive. Should the streams in which num- 

 bers of Paraponyx larvae reside, during a season of drouth become 

 entirely dried up, the sudden and doubly renewed efforts of these 

 animals, in their " struggle for existence," would doubtless so 

 operate upon the spiracles and trachea as to necessarily lead to 

 their perfect development and functional activity. It is a familiar 

 occurrence that the wings of moths, butterflies, etc., when first 

 they leave the chrysalis cover, are short, sac-like, bodies ; but by 

 their energetic movements speedily develop into their character- 

 istic forms. This is accounted for in the following manner: 



