SAEGASSUM, 



[ 676 ] 



SCALES. 



pi. 7. fig. 56, and pi. 13. fig. 113; Endliclier, 

 Gen. riant. Supp. i. nos. 474-1. 



Fig. 624. 



Fig. 625. 



.^^^sK^fflrr^, 



% 



Sarcoecyplius Ehiharti. 



Fig. 624. Perithoete and perigoue opened, stowing the 

 young sporange emerging from the epigone. Magnified 

 25 diameters. 



Fig. 625. Perichiete and perigone opened, show ing the 

 ba>e of the seta surrounded by the epigone. Magmlied 

 10 diameters. 



SAP.GAS'SUM, Ag.— A gemis of Fuca- 

 cete (Fucoid Algae), gulf-weeds, known 

 from the allied sea-weeds by its stalked 

 globular air-vessels. The receptacles are 

 small, linear, and mostly clustered at the 

 base of branches, and pierced by numerous 

 pores leading to conceptacles, containing 

 spore-sacs and clusters of autheridia (see 



FUCACE^). 



BiBL. Harvey, Brit. Mar. Alg. p. 14, 

 pi. 1 A ; Greville, Alg. Brit. pi. 1. 



SCALAEIFOEM VESSELS. See 

 Spiral Strtjctubfs. 



SCALES OF Fishes. — These bodies 

 were formerly regarded as epidermic ft)rma- 

 tions, analogous to the nails, &c. of the 

 higher animals, which later observations 

 have shown not to be the case. 



Each scale is contained in a distinct sac 

 of the skin or cutis, covered externally with 

 its pigment-layer and epidermis. The cutis 

 itself consists of interlacing fibres of areolar 

 tissue with formative cells. The piiiment- 

 layer is composed of elegant pigment-cells 

 with long prt)cesses. Immediately above 

 the upper surface of the scales lies a very 

 fine membrane, distinct from the cutis, in 

 which the impressions of the irregularities 

 of surface existing upon the scales are 

 visible. 



In some fishes, as the eel, the scales do 

 not project beyond the surface ; hence the 



eel is commonly supposed to possess no 

 scales. They are easily seen, however, in a 

 dried piece of the skin, mouutt'd in balsam, 

 covered by the skin with its pigment-cells 

 (PI. 22. fig. 19), the whole forming a very 

 beautifid object. 



In many of the common cycloid fishes, as 

 the roach, dace, &c., the scales projects pos- 

 teriorly from the sm-face, carrying before 

 them the thinner and closely applied outer 

 layer of the cutaneous sac, whilst the ante- 

 rior portion of the sac extends into or is 

 formed bj' the under portion of the cutis. 

 In these fishes also, the portion of the cutis 

 situated beneath the posterior projecting 

 portion of the scales contains a large num- 

 ber of very thin and minute crystals, to 

 which the silvery lustre of the skin is owing, 

 and which often exhibit very beautifully the 

 colours of thin plates. 



The signification of the various parts of 

 structure of the scales has not been satis- 

 factorily determined ; hence we must con- 

 fine our remai-ks to simply pointing out the 

 structural peculiarities. 



Most scales consist of two portions, — an 

 under, composed of numerous layers made 

 up of very fine fibres taking various direc- 

 tions, and best seen by scraping away the 

 upper portion of the scale after maceration 

 in dilute acid (PI. 22. fig. 11 a). The upper 

 portion consists of concentric plates, the 

 margins of which give rise to the concen- 

 tric lines so frequentlv seen in the scales 

 (PL 22. tigs. 6, 10, 22, 23, &c.). These lines 

 correspond to the margins of the layers, and 

 often present a nodular or crenate appear- 

 ance (fig. 116); and towards the middle 

 of the scales they are frequently interrupted 

 and irregularly curved (fig. lie). The sub- 

 stance of the upper portion appears to be 

 structureless. 



In a transverse section, the projecting 

 margins of the laminae belonging to the 

 upper portion of the scale are seen as so 

 many teeth (PI. 22. fig. 12.) 



INIany scales also exhibit radiating lines 

 (PL 22. fig. 23), corresponding to furrows 

 in the upper portion of the scales; these 

 are sometimes closed above, so as to form 

 tubes, and have been regarded as nutritive 

 canals. 



Near the centre of some scales, as those 

 of the perch, are numerous rounded corpus- 

 cles or solid bodies, imbedded in the sub- 

 stance of the upper portion of the scales 

 (PL 22. figs. 6a & 7). At the posterior 

 portion of the same scales are often seen 



