6 



and first pair of cirri, which are seated at a sbrrt 

 distance from the second pair, the others b-mfj 

 close together and forming a semicircle r>und the 

 mouth. Each cirrus is divided into two branchns 

 and each branch is composed of a tireat many 

 segments, so that there are twenty-four long ^nd 

 flexible arms adapted for securing prey ; and the 

 entanglement of any passing object is still further 

 assisted by the presence of a number of long 

 spines or bristled with «hich each segment of the 

 cirri is furnished. "When the cirri are protruded 

 in search of food the two branches of each cirrus 

 diverge, and as they are retracted theii tips are 

 curled inwards, and this beautiful apparatus, 

 alternately thrown out and drawn in with threat 

 rapidity, like a many-6Dgered hand or a d*licHte 

 casting net, catches any objt^ct suitable for food 

 that comes within its range, closes over it, and 

 conveys it to the mouth. These movements of the 

 cirri: the opening and closing of the operculir 

 valves ; and, in the case of the stalked ppt-ciep, the 

 contraction and elongation of the peduncle, are nil 

 regulated by a muscular system receiving nervea 

 from various ganglia. The shell of the stalked 

 barnacles is generally formed of valves connecfwd 

 by slips of membrane. If we take a commf>Q 

 " ship-barnacle " {Lepas atiatifera) for the purpnge 

 of illustration, we find that it consists of five 

 valves, four of which are disposed in pairs, 

 while the fifth, which is long and narrow, serves as 

 a hinge uniting the other valves. This is called 

 the carina. The upper pair of openingr valves are 

 the terga ; the lower pair the scuta In front an 

 opening in the mnmbraDous lining allows thn cirri 

 to be protruded, and f ■ >r this purpose the val ves on 

 each side of the opening are moveable, and are 

 regulated by powerful muscles. In the sessile 

 barnacles the opercular valves are placed within a 

 conical shell composed of valves answering to tho-^e 

 which form the carapace of the Lepadidae. but 

 instead of being united by strips of membrane 

 more or less flexible, the compartments of these 

 shells are firmly soldered together. The two 

 opercular valves move up and down within the 

 cone, and open for the protrusion of the cirri. At 

 other times they are tightly closed, and fit with 

 the most perfect accuracy. When we examine the 

 shell of a sessile cirripede, especially if it be one 

 of the larger species, say Balanus tintinnabuhtm, 

 and observe its compact and massive structure, it 

 is not easy to understand how its gradual enUrge- 

 ment is effected. To all appearance it consists of 

 a single piece. In reality it is formed in compart- 

 me-'ts so strongly welded together that they defy 

 all attempts at separation ; and I exhibit speci- 

 mens which have been boiled for eight hours in 

 potash without betraying the slightest weakness 

 in the sutures. But an effect was produced on a 

 smaller shell attached to one of these specimens, 

 and this, after boiling, yielded to slight pressure 

 and separated, at the lines of suture, into the six 

 compaiimenls of which the shell is composed. 

 Darwin states that the tubes formed by the septa 

 dividing the outer and inner laminae of the walls 

 of the shell are occupied by threads of corium, and 

 that create of corium also run into each suture 

 between the compartments ; and he accounts for 

 the difficulty and almost impossibility of separating 



the compartments in sorao species of Ralanua by 

 supposing that (to quote his own words) "compart- 

 ments in such ca-esare joined slopg the li dp of euture 

 by tissue which mustbeinacftlcitiedstate.but which, 

 nevertheless, continues to grow by intersusception ; 

 in other words, that the tips of the complicated 

 ridges and points interlocking on the lines of 

 ?uture are not separated from each other by films 

 of cerium or simple animal matter, but are 

 actually united by corium in a calcified, yet still 

 growing condition." The number of compart- 

 ments may be eight, six, or four, according to the 

 species, but all agree in thepatternson which they 

 are formed. These are three in number and are 

 always arranged in a definite order. In each 

 compartment there is a central portion called the 

 wall or parietal portion, furnished with sides or 

 wings, which may be either (1) Raf^ii overlapping 

 the adjoining compartments; nr (2) Al:e. overlaid 

 bv the adjoijing radii ; or (3) there may be an 

 ala on one and a radius on the other. I exhibit 

 specimens of each of these forms, and, as the 

 specimens are small, I have copied from Darwin's 

 Monograph diagrams of their shape, snd the mode 

 in which they fit into each other. Another 

 diagram shews the arrangement of the six com- 

 partments in Balanus compHred with the type- 

 arrangement of eight compartroerts in OctomeriSt 

 the latter being arranged thus: At the two ends 

 of the shell are compartments resembling each 

 other, having alai on both .«ides of the parietea. 

 These compartments are called respectively the 

 carina and the rostrum, and ar« constructed on 

 the second of the patterns I have descrJhed. On 

 eifher side of the rostrum is a rostro-lateral com- 

 partment, having a radius on each side of the 

 parietal portion. This is after pattern No 1. Next 

 to these are the lateral compartments, and oa 

 either side of the carina is rarino-lateral compart- 

 ment, having radii on their carioal and ahe on 

 their rostral sides, being fashioned after pattern 

 No 3. In Balanus the two lostro-lateral com- 

 partments are combined with the rostrum, thus 

 reducing the number of compartments in this genus 

 to six The upper portion of the shell is strengthened 

 by an internal hoop called the sheath. This is 

 formed by a thickening of a portion of the inside 

 surface of those compartments which overlap the 

 alae, so as to form a ridge into which the edges of 

 the alae are received. To the lower edge of this 

 sheath the opercular membrane is attached. The 

 membrane is continuous with the membranous 

 lining of the sack within the shell Inside this 

 sack the body of the animal is suspended, a portion 

 of the body being attached by muscles to the 

 opercular valves These valvesarefourin number ; 

 a pair of Scuta and a pair of Terga, but each 

 scutum is articulated to the adjoining tergum so 

 firmly that in appearance there are but two valves. 

 A furrow in the margin of the scutum receives the 

 inflected margin of the tergum and in most cases 

 the border of the scutum is also reflexed and lodges 

 in a furrow in the upper part of the tergum, which, 

 again, is bordered by a ridge. In most of the 

 genera the walU of tV>e compartments are not 

 solid, but, as in Bnlanus. are composed of an outer 

 and inner lamina separated by septa, which are 

 beantifoll; denticulated, and between these septft 



