DWELLINGS 1603 



There is, for example, the Macropus viridi- 

 auratus, or paradise-fish, which blows air bubbles in 

 the mucus produced from its 'mouth. This mucus 

 becomes fairly resistant, and all the bubbles impris- 

 oned and sticking side by side at last form a floor. 

 It is beneath this floating shelter that the fish sus- 

 pends its eggs for its little ones to undergo their early 

 development. 



Certain tubicolar annelids, whose skin furnishes 

 abundant mucus which does not become sufficiently 

 hard to form an efficacious protection, utilize it to 

 weld together and unite around them neighboring 

 substances, grains of sand, fragments of shell, etc. 

 They thus construct a case which both resembles for- 

 mations by special organs and manufacture by the 

 aid of foreign materials. The larvae of Phryganea, 

 who lead an aquatic life, use this method to separate 

 themselves from the world and prepare tubes in 

 which to dwell. All the fragments carried down by 

 the stream are good for their labors on condition only 

 that they are denser than the water. They take pos- 

 session of fragments of aquatic leaves, and little 

 fragments of wood which have been sufficiently long 

 in the water to have thoroughly imbibed it, and so 

 become heavy enough to keep themselves at the bot- 

 tom, or at least to prevent them from floating to the 

 surface. It is the larva of Phryganea striata which 

 has been best studied; those of neighboring species 

 evidently act much in the same way, with differences 

 only in detail. The little carpenter stops a fragment 

 rather longer than his own body, lies on it and brings 

 it in contact with other pieces along his own sides. He 



