248 



BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



Proboscis provided vnt\x central stylet and tbree pouches of 

 accessory stylets. Central stylet and basis slender and of about 

 equal length (PL 16, tig. 100). 



Specimens but 10 mm. in length, and evidently very young, had 

 only 3 or 4 ocelli in each marginal group and 4 or 5 in each cerebral 

 cluster (PI. 25, fig. 196). All had the three pouches of accessory 

 stylets, however. An interesting correlation between size, number 

 of ocelli, and size of stylet apparatus is illustrated by the following 

 measurements : — 



The smallest and evidently youngest individuals therefore, with 



the smallest number of ocelli, had the 

 central stylet but little more than half 

 the length of that of the larger indi- 

 viduals, while the length of the basis of 

 the central stylet varied nearly three 

 fold between the smallest and largest 

 individual. This correlation does not 

 continue, however, in individuals above 

 medium size, for after the worms have 

 attained a length of about 25 mm. there 

 is compai'atively little increase in num- 

 ber of ocelli or size of stylet apparatus, 

 although the average in both these par- 

 ticulars is undoubtedly greatest in indi- 

 viduals of the largest size. The probos- 

 cis is usually provided with about 15 



nerves. 

 Fig. 53.—Amphiporus imparispi- Cerebral sense organs small, situated 



nosus. Outline of head, showinsr ■,^ • c , p i 



position of ocelli. ^^ell in fi'ont of bram. 



