628 HAROLD HEATH, 



if the water be agitated until they are distributed equally through 

 the jar they will collect at the lighted side within fifteen minutes. 



As has been seen strong cilia develop within 24 hours after the first 

 cleavage and in a 36 hour embryo they beat with a rapidity of 

 about 100 times per minute. This continues for five days and when 

 the larvae are liberated it would be supposed that with such a power- 

 ful locomotor apparatus they were destined to a free swimming 

 existence of considerable duration ^). But in apparently nearly normal 

 environment this is not so. In almost every case when small lots 

 were separated from the main company they were found to settle 

 within a period lasting from fifteen minutes to three hours. That 

 this is apparently a correct and normal characteristic is shown by 

 the movements in another Chiton. It probably belongs to the genus 

 Trachydermon and as in the case of Ch. polii carries its eggs in the 

 mantle furrow. In several instances I have found scores of small 

 Chiton within a very small distance of the parents, showing that the 

 free swimming stage could have been only of the briefest duration. 

 Certainly the chances of destruction are greatly lessened where the 

 free - swimming stage is short and it seems quite probable that a 

 suppression of this period of the Chiton's existence is a provision to 

 insure greater safety and consequently to bring a greater number of 

 individuals to maturity. 



The movements of the larvae are of considerable rapidity, the usual 

 rate as based on observations of nineteen specimens being 8 — 10 cm 

 per minute. In addition to this progressive motion is one from right 

 to left, the animal thus moving in a loose spiral. 



The flagella at the anterior end of the body at the centre of the 

 velar area are generally two in number though as many as four occur. 

 One is generally longer than the other, and after treatment with 

 fixing agents they are seen to be compound, being composod of a 

 number of lesser flagella. As the animal swims through the water 

 these are whipped about in various directions , much like the great 

 antennae of some of the Crustacea, the base being held comparatively 

 rigid in each case. At least one of its functions appears to be that 

 of a sense organ. I have frequently noticed that the larva turned 

 aside from a foreign object as soon as it was touched by the flagella 

 and in such cases the body itself never came in contact with the obstacle. 



1) It appears very probable that the movements of the cilia 

 previous to the free swimming stage aid very materially in the process 

 of respiration. 



