81 B-OLA88 I 



AKTHOZOA TETRACORALLA 





/// / 

 or dissepiments, mxi ////// well^nctrbed^ fi/>fn>-nf/i/ /'//////'</ >/w/. 



The Tetnn-iii-iiltii are especially characteri>ed by the possession <>f foui 

 principal or primary septa, between which four set- of new >epta ;uc subse- 

 quently developed. The four principal septa are sometimes of c<|ii;il pi-opor 

 tions. when they may bo either stouter ami longer than the others (>'/// 

 thinner and shorter (Omphyma) } or they may In- of une,|u;d proportions. Of 

 the two principal septa which lie in the longitudinal axis of tin- corallum. nin- 

 (called tlie 1-iin/itnil tH-jifinii) is fre(juently situated in a depre ion or furrow 

 known as tin- t'<*.<nli (Fig. 104); while the other or <>//////,/ .///////, is either 

 normally developed, or is more or less reduced. Occasionally the counter 

 septum is placed in a fossula, while the cardinal septum is normally developed . 

 but the two laterally disposed or nlur >>y/" are always e|iial in sixe. The 

 remaining septa not infrequently exhibit a well-marked radial arrangement, in 

 which the longer and more strongly 

 developed usually alternate with the 

 shorter and less strongly developed. 

 New septa, according to Kunth and 

 Dybowski, are inserted in the follow- 

 ing order. First, a new septum is 

 given off on either side of the cardinal 

 septum (Fig. 104, A), and takes up a 

 position parallel with the alar septum. 

 This leaves an intermediate space 

 between the cardinal and the newly 

 formed septa, which becomes filled, 

 however, by the repeated insertion of 

 new septa one above the other in the 

 same manner as the first ; and hence 

 they diverge from the cardinal septum, 

 as they grow upward, in a pinnate 

 fashion. Likewise the two counter te1 ' s '' 1)tnl 

 quadrants lying between the alar and 

 counter septa become occupied by lamellae which are given off from the alar 

 septa, and gradually arrange themselves parallel with the counter septum. 

 The mode of growth in the Tetrawratla will be readily understood on inspecting 

 the surface of such specimens whose septa are visible on the exterior, or whose 

 wall is readily removed by corrosion or polishing. One may then note three 

 distinct lines extending from the calicinal margin to the base ; these mark the 

 cirdinal and the two alar septa, from which the other pinnately branching 

 septa are directed obliquely upward (Fig. 105). The order in which the septa 

 are given off in the four quadrants is indicated by the numerals in Fig. 104. 



Many of the Tetrwnrnllii multiply by sexual reproduction, and occur only 

 as single individuals ; asexual reproduction takes place usually by calicinal, 

 more rarely by lateral gemmation, and results in dendroid or massive colonies. 



Dissepiments are generally abundantly developed between the septa, 

 which latter are compact, and the upper edges of which are either smooth or 

 serrated. Sometimes the dissepiments fill the whole interior with a vesicular 

 tissue, and the central visceral cavity is frequently entirely partitioned off by 

 horizontal, inclined, or funnel-shaped tabulae. The wall is usually composed 



MI nnjili iiUu in 1i IIH'I inn r- 

 !/: nut ii in, K. aii'l II. ' u- 

 honilVrous Limestoiif ; 

 Tom nay, Bi-l^iuin. -/]. 

 A. Cun'linal si-plum ; ij, 

 s, Alar 



I 'I... 105. 



Zaphrentif 

 Bill. Onlovician : 

 cinnati, Ohio. Natural 

 size. 



