242 



\'Ki;Ti';ni;ATF. animals. 



to anothei- order) is the couversiuii of the l)ii(lies of tlie vertelme into 

 bone carried further tliaii this. 



2. The integument usually develnjis scales, ami the.se in the great 

 majority of cases ai-eof tlie forms kntiwn as "cycloid " and "ctenoid," 

 the former being circular or ellijitical horny plates, with jjlain mar- 

 gins ; whilst the latter have their hinder margins cut into comb-like 

 projections or fi-inged with spines (tig. I(i4, a, h). 



3. The antifriiir mij jiimturiiir limJis (fig. 174) are u.sually, but not 

 always, present, and "\\hcu developed tliey are always in the form of 

 tins. These tins maj' be sujiported by "sjiinous rays " or "soft I'ays," 

 or by both. The spinous rays are simjile undivided bony spines 

 which taper to a jmint. The .soft ravs are doulil^' divided, splitting 

 up tfjwarils their extrenuties into a nundier of secondary rays, 

 and being also divideil by transverse joints into mimerous short 

 ]iieces. 



4. Besides the "paired" lins whicli re] resent the limbs, there is 



Fig. 17-1. -Tl)i' Orirl {i;,i:hi!!vin,-rhmi-). 



also a series of iiiipiiinil or " meili.an " tins, the rays of which are 

 supported upon a series of dagger-sh.ijied bones, dee]ily plunged in 

 the Hesh in the middle line of the body, ami known as the " inter- 

 spinous " bones (tig. Kio). The median fins (fig. 174) are variable in 

 number, but when fully develojied they consist of one to three tins 

 on the back (the dor.sal tins), one or two on the ventral surface (the 

 anal hns), and oiu^ chithing the p(isterior extremity of the bod}' (the 

 caudal tin, or tail). In all the 7'i'/rnsti'/\ the caudal fin has the shape 

 c:dled " homocercal " — that is to say, it consists of two equal lobes 

 — and the vertebi'al cobuun is not ]irolonged into the U])per lobe 

 (tig. 171). 



5. The heart consists of two cavilies, an .•inricle and a ventricle, 

 but the hii/lms iirterin-iiiK is not iliythinically conti-ictile, and is 

 sejiaratcil from thi' ventricle by only a single pair of valves. 



(;. The resjiiratoiy organs are in the form of free, cond)-like, or 

 t idled i^ills, ciiclosed in two cavities |il;ici'd on the sides of the neck. 



