130 



ZOOLOGY 



sessile and enclosed in shells ; but their peculiar habits 

 have given rise to certain peculiarities in reproduction. 

 They are hermaphroditic; i.e. both male and female germ- 

 cells occur in the same individual. Despite this fact, 

 dwarf male individuals are occasionally found inside the 

 shell of the barnacle ; these are known as " complemental 

 males." The general form of the barnacles has also be- 

 come greatly modified by their 

 sessile habit, so that they 

 were long regarded as mol- 

 lusks, until it was shown that 

 the larvae are almost exactly 

 like those of other Ento- 

 mostraca. 



Trilobites 1 are extinct giant 

 ' Entomostraca, closely allied 

 to Branchipus. They were 

 immensely abundant in early 

 geologic times, and their re- 

 mains form a large part of 

 certain rocks. They had a 

 segmented body, with bifid 

 appendages and long antennae, 



FIG. 121. - A restoration of the and their compound eyes were 



borne on the great frontal 

 shield. Some of them were 

 nearly half a metre long. 



ventral aspect of a Trilobite. 

 Note in particular the charac- 

 ter of the appendages. After 

 Beecher. 



Having three lobes. 



