®k Journal of ipai[tnc iootojjii 

 and Jffipjujojjii : 



A PLAINLY WORDED BIOLOGICAL QUARTERLY. 

 VOL. I. No. 4. SEPTEMBER, 1894. 



THE LIFE-HISTORY OF THE ROCK BARNACLE, 



' (BALANUS), 



BY THEO. T. GROOM, F.Z.S. 

 (Part I). 



EVERY visitor to the sea-side is familiar with the appearance, if 

 not with the names of the " Barnacles " and " Acorn-shells ". 

 The spar cast up by the waves, with its forest of strange-looking 

 stalked shells, has often provoked the curiosity of those unacquainted 

 with the secrets of Natural History. Almost anywhere along our 

 rocky shores the countless myriads of small whitish conical shells 

 firmly fixed on the rocks between tide-marks, give quite a dis- 

 tinctive appearance to the landscape. These small creatures ap- 

 parently so rigid and still, have a wonderful life-history. In 

 mediaeval times it was seriously maintained that the barnacle was 

 only the young of the barnacle-goose. One observer desirous of 

 handing down his name to posterity as an original discoverer, 

 actually saw the young bird inside the shell of the Crustacean, 

 and records his observations in the following words : — " In every 

 shell that I opened I found a perfect sea-fowl, the bill like 

 that of a goose, the eyes marked, the head, neck, breast, Avings, tail, 

 and feet formed, the feathers everywhere perfectly shaped and 

 blackish coloured, and the feet like those of other water-fowl to my 

 best remembrance." — (Quoted in J. V. Thompson's " Zoological 

 Researches "). 



The young Barnacle, however, leaves its egg-shell in a much 

 less highly organized form than that of a young bird. It hatches 

 as a typical Nauplius, a larval form characteristic of the Ento- 

 mostraca or lower Crustacea. The Nauplius of the ordinary rock 

 Barnacle (Balanus) after throwing off its first cuticle is shown in 

 PL viii, Figs. 1 and 12. It has a shield-shaped carapace, and is so 

 transparent when living that most of the internal organs can be 

 easily made out. The anterior angles of the shield are prolonged, 

 as in nearly all Cirripede Nauplii, into a pair of horns, which are 



