262 



THE INFANCY OF ANIMALS 



parent shell that is to protect the soft body of the mussel 

 for the rest of its life. 



The comparison of the glochidium stage with the free- 

 swimming stage of the fresh-water mussel Dreissensia, or 

 of the oyster, it should be remarked, is 

 not exact, for the glochidium has already 

 passed through the shell-less stage of the 

 oyster within the egg while enclosed within 

 its parent's gills : thus furnishing another 

 illustration of the different periods of 

 development at which post-embryonic 

 life begins. The little yoldia, and the 

 oyster and the young dreissensia all agree 

 in having excessively frail, transparent 

 bodies, microscopic in size, and furnished 

 with rows of vibratile threads, the move- 

 ments of which drive the body through 

 the water, till a suitable place for settling 

 down is found, when all further roaming 

 is at an end. 



Life with the glochidium hangs indeed 

 by a thread, and the same is true for a 

 season with the young of spiders. Not 

 the dreadful things which make the blood 

 of the householder run cold, but of spiders 

 which live a healthy outdoor life. My 

 readers must often have seen the fields 

 in the sunlight of an early October 

 morning glistening with the sheen of gossamer threads : 

 all but invisible, and with no apparent source of origin. 

 And to many it may be news to learn that these threads 

 are spun by hundreds of thousands of tiny spiders who 

 are seeking to explore the world. The device they adopt 



A YOUNG SPIDER 

 SPINNING GOS- 

 SAMER THREADS 

 PREPARATORY 

 TO TAKING 

 FLIGHT. 



