200 BULLETIN OP THE BUREAU OF FISHERIES 



As will be seen, the largest number of forms is found in the group of barnacles. 

 (Figs. 2 and 3.) These organisms vary greatly ia size and shape, many kinds never 

 growing more than one-fourth inch in diameter, and often not so high. Some 

 species, however, notably those that attach on ships in tropical waters, grow to a 

 very considerable size — 4 inches in diameter and 6 inches in height. Very frequently 

 they are found growing one upon another, so that the height of a cluster occasionally 

 may reach 8 or even 10 inches. Most barnacles are protected by means of hard 

 calcareous plates, which surround the animal, forming a sort of shell. These plates 

 vary in number, with the kind of barnacle, from four to very many; but the more 

 common forms (Balanus) all have six plates or compartments forming the walls of 

 the shell and two pairs of plates that comprise the top or covering of the shell, and 

 which are arranged like valves. Between these valves the animal extends its thoracic 

 appendages when feeding. (Fig. 4.) This peculiar habit has given rise to a popular 

 description of a barnacle as an "animal which stands on its head and kicks its food 

 into its mouth." Some barnacles, however, do not form heavy calcareous shells 

 and are very much elongated. (Fig. 5.) These are commonly called "gooseneck" 

 barnacles and include the last six species of barnacles listed on page 199. Since the 

 "neck" or stalked portion of this type of barnacle is not protected by shelly structure, 

 such growths fall off upon the death of the organism; but all other types of barnacles 

 leave behind them their shells or houses, which frequently persist for many years if 

 not forcibly removed. 



Barnacles have a complicated hfe history. The eggs are fertilized within the 

 body chamber of the adult and held in lamellar folds until the young are hatched. 

 The almost microscopic larval organism is free-swimming, with three pairs of ap- 

 pendages and a single median eye, and is known as the "nauplius." (Fig. 6 A.) 

 After a period varying from 1 to 10 days, or more, these nauplii metamorphose 

 into tiny bivalved forms called the "cyprid" larvae. (Figs. 6 B, C, and D.) At 

 this time the larval barnacle has six pairs of appendages, like the adult, and two 

 long antennse with many sensitive hairs or bristles. The median eye is sometimes 

 lost, and paired compound eyes are always present. 



These young barnacles, resembling miniature clams, float and swim about for a 

 considerable time, often for two or three months, and finally attach by use of appar- 

 ently adhesive pads on the tips of the two antennse. (Figs. 6 B and G.) After 

 attachment, they metamorphose into the adult stage, miniature at first but grow- 

 ing rapidly to full size. At the time of this radical change the eyes apparently 

 are lost in some forms. It is the stiidy of these cyprid larv<B at the time of attach- 

 ment, of course, which is of fundamental importance in an investigation of the 

 fouling of ships' bottoms. 



It is of interest to note that of the 150 species of barnacles listed by Charles 

 Darwin in his monograph of 1853, only 15 kinds have been found on ships examined 

 for this investigation, and that all of the commonest are typical shore forms, normally 

 inhabiting shallow water (and rarely living at depths in excess of 10 fathoms), such 

 forms as are found in most harbors and sheltered coastal areas. 



The hydroids are the next most numerous animal group, with 15 tji-pes found 

 during the investigation. Hydroids usually are colonial in their growth and have 

 an even more complicated life history than do the barnacles. These growths begin 



