LOTN'S LAEYA. 



363 



Behind it is continued into an indifferent terminal portion equivalent 

 to the whole body of the adult. 



At the apical region of the larva (fig. 294, Sp) there is a 

 thickening of the ectoderm, which is called the apical plate. This 

 represents the rudiment of the cerebral ganglion (apical ganglion), 

 and gives off nerves to either side. The wide mouth (0) has a 



FIG. 291. Development of Polygordiug (after B. Hatschek). a, Young larva ; Sp, apical 

 plate with pigment spot ; frw, prse-oral circle of cilia ; O, mouth ; Poic, post-oral circle 

 of cilia; A, anus; Ms, mesoderm ; JOT. head kidney. 5, Older larva with commencing 

 segmentation of the body, a second limb is developed in the head kidney, c, Older stage. 

 The body is elongated to the form of a worm, and divided into a number of metameres ; 

 HWk t posterior circle of cilia; Af t eye spot; F, tentacle. 



ventral position, and leads into an alimentary canal, which opens 

 at the posterior end of the body (A). In front of the mouth there 

 is a strongly developed circle (prscoral) of cilia (Prw) ; and behind 



