606 



ZOOLOGY 



SECT. 



The larvae of several species of Trilobites have been found in the fossil state. 

 In some of these the body consists only of carapace and pygidium in the youngest 

 stages, and the thoracic segments are subsequently intercalated in regular order. 

 In other species the earliest stage has the form of a rounded plate, the posterior 

 portion of which elongates and segments to form the thorax and abdomen. 



FIG. 478. Triarthrus becki, x2^. A, ventral surface with appendages; Ep, metastome ; 

 Hy, hypostonie. B, second thoracic appendage, en. endopodite ; ex. exopodite xl'2. (From 

 the Cambridge Natural History, after Beecher.) 



Nothing is known of the larval appendages, and none of the stages hitherto dis- 

 covered can be considered as nauplii. 



The precise systematic position of the Trilobites is uncertain, but their 

 nearest affinities seem to be, on the whole, with such Branchiopoda as Apus : 

 but the relationship is by no means a close one. 



