86 



Zoology. 



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

 glance, hardly be regarded as Crustacea at all, so much 

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

 of life. The 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 balanoi- 

 des) abounds on every rocky 

 shore from extreme high-water 

 mark to deep water, and the 

 student can, by putting a group 



fig. ioo.-a barnacle. Balanus of tbem in sea water, observe the 

 porcatus. Natural size. opening and shutting of the 



valves and the movements of the hairy appendages. 



The metamorphosis of the barnacle is remarkable. After 

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



Fig. 101.— Nauplius of Bal- 

 anus balanoides. Much 

 enlarged. 



Fio. 102. 



-Pupa of Lepas. 

 enlarged. 



Much 



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 (tlie 



