198 EVENINGS AT THE MICROSCOPE. 



former was only — J-yth of an inch in length, these have 

 attained to a length of T \jth of an inch. Yet this increase 

 is observable in no other dimension than that of total 

 length ; and this is due to the development of the terminal 

 spine of the shield, which is now much produced, and cut 

 into minute teeth. The anal fork is also attenuated, 

 lengthened, and bent abruptly downward at the base, 

 where it is very mobile; another bend in the middle 

 throwing the extremity into the horizontal again. The 

 delicately membranous pouch-like proboscis is more 

 clearly seen beneath the breast, the extremity of which 

 is directed backwards. In front of this organ there are 

 two decurved very mobile bristles, set on pedicles, or 

 stalks, the whole closely resembling the internal antennae 

 in the higher Crustacea. The lateral horns or external 

 antenna? appear to terminate in a very delicate brush of 

 hairs, which does not seem to be capable of being 

 protruded. 



The little animals in this state swim, generally, back 

 downward ; though they frequently assume a perpen- 

 dicular position, both direct and reversed. I see them 

 now occasionally resting on sea- weeds and Diatomacece, 

 though the limbs seem even worse fitted than before for 

 crawling, since the spines or bristles with which they 

 are fringed are much increased in length, especially on 

 the third pair. 



A specimen nearly twice as large as these last affords 

 us an opportunity of tracing the Barnacle to another point 

 of its transformations. The modifications are chiefly in 

 the proboscis and the anal fork. The former now points 

 directly downwards ; is furnished with a pair of minute 

 spines on its anterior side, and with a terminal hook ; 

 while its posterior side is set with strong vibrating cilia. 

 The anal fork is greatly increased in dimensions, has its 

 edges armed with spines articulated to its surface, and is 

 marked with longitudinal lines which resemble corruga- 



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