86 



ZOOLOGY. 



Order 1. Cirripedia. — The barnacles would, at a first 

 glance, liardly be I'egardcd as Ci'ustacea at all, so much 

 modified is the form, owing to their fixed, parasitic mode 

 of life. Tlie barnacle is, as in the common sessile form 

 (Fig. 100), a shell-like animal, the shell composed of sev- 

 eral pieces, with a conical movable lid, having an opening 



through which several pairs of 

 long, many-jointed, hairy ap- 

 pendages are thrust, thus cre- 

 ating a current which sets in 

 towards the mouth. The com- 

 mon barnacle {Balanus lalanoi- 

 des) abounds on every rocky 

 shore from extreme high-water 

 mark to deep water, and the 

 student can, by putting a group 

 Balanus of tlicm in sea-watcF, observe the 

 opening and shutting of the 

 valves and tlie movements of the hairy appendages. 



The metamorphosis of the barnacle is remarkable. After 

 leaving the egg, it swims about as a minute Nmiplius or 



Fio. 100.— A barnacle 



porcatus. Natural size. 



Fia. 101.— Nauplius of Bal- 

 amis halanoides. Much 

 enlarged. 



Fia. 108.— Pupa of Lepas. Much 

 enlarged. 



larva (Fig. 101), with three pairs of legs. Finally the larva 

 attaches itself by its antennas to some rock, and now a 

 strange transformation follows. The body and legs (the 



