HARD W I CKE ' S S CIE NCE ■ G O SSI P. 



H5 



GRAPHIC MICROSCOPY. 



By E. T. DRAPER. 



No. XIX. — Section of Shell of Barnacle {BaJanus sulcatus). 



HE cirripeds, or 

 barnacles, in their 

 adult condition have 

 a curious dissimi- 

 larity of form. The 

 Lepadidse appear as 

 p edunculated 

 masses, and elegant 

 groups of these 

 "necked barna- 

 cles" are found on 

 floating timber or 

 wreckage. The 

 fixed stem, or 

 peduncle, is often 

 several inches in 

 length, thick in pro- 

 portion, freely flexi- 

 ble, of peculiar 

 tough texture, 

 possessing voluntary movement, and surmounted or 

 tipped with a conical articulated shell containing the 

 animal, from the apex of which emerge the " cirri.'' 

 Of the same family, although so unlike in appearance 

 are the Balanidoe, popularly known as "acorn shells," 

 sessile, the creature included in a compact although 

 somewhat moveable calcareous domicile, firmly at- 

 tached to the surface of constantly submerged rocks, 

 and the bottoms of ships, enjoying, as the vessel 

 drives through the seas, the luxury of a vagrant life, 

 and with its singular and well-adapted casting net, 

 collecting abundant food from the scums and shoals of 

 microscopic organisms. The close relationship between 

 the Lepadidae, with their long flexible stems, and 

 the Balanidas in their shelly boxes, is detected in the 

 perfect identity of the larval free swimming condition. 

 At this point their similarity is manifest. When the 

 perfection of this state is attained, the little creature 

 seeks a point of attachment : the bottom of a vessel, 

 floating substances, or the solid rock, and fixing itself 

 by an outpouring of glutinous cement, in the one case 

 No. 247.— July 1885. 



prolonged into a stem-like flexible stalk, in the other 

 fixed in a shelly pyramid. 



Compared with the brilliant hues and elegant 

 configuration of "shells" in all their interesting 

 varieties, as appreciated by collectors, the appear- 

 ance of a barnacle scraped from the bottom of a 

 vessel has externally no great beauty, or attraction ; 

 but, like many apparently obscure objects, when 

 subjected to microscopical examination, it reveals 

 structural peculiarities and adaptation of very 

 significant interest. 



In the sessile group of the Cirripedia, of which 

 Balanus sulcatus and B. tinlinnahulum are the most 

 prolific and common forms, unlike the compact and 

 entire solidity of a shell as generally understood, it 

 is composed of four or more thick external articu- 

 lated conical plates, supported on a flat adhesive 

 base, the apices running upwards. Within and 

 enclosed in these are thinner and more moveable 

 processes interlapping, and when reaching the 

 summit so delicately fine as to become a mere slit of 

 exquisite adjustment for the extrusion of the cirri, or 

 curly filamentous appendages ; these flash out, for 

 the collection of food and purposes of aeration, and 

 when as suddenly retracted the delicate edges of this 

 sensitive operculum hermetically close the aperture, 

 and the creature within. The growth of these lami- 

 nated plates of shell is seen by perpendicular and trans- 

 verse ridges, showing expansion in every direction. 

 The base of fixture is a flat foundation of accumulated 

 calcareous secretions, and in specimens taken from 

 the hulls of ships, more or less incorporated with the 

 paints and deadly oxides of metals used to discourage 

 their accumulation. But balani generally succeed in 

 eluding these ingenuities. 



If a shell be broken into, near the base, inside, 

 above the floor of attachment (the point of greatest 

 resistance), a part may be seen corrugated, and having 

 a columnar appearance ; if a slightly oblique horizontal 

 thin section be cut through this point, the apparently 

 uninviting fragment reveals a structure of adaptability 



