ANATOMY OF VERTEBRATES. 7 



Thus vertebrates might be binarily divided into oviparous, i. 

 II. III., and viviparous, iv. ; into anallantoic or branchiate and 

 allantoic or abranchiate ; into HamatoUteniial,'^ having the four- 

 chambered heart, spongy lungs, hot blood, and Hmaatocryal,'^ 

 having less perfect breathing organs, less complex heart, with cold 

 blood ; and each of such divisions are artiticial and convenient. 

 It suits my present purpose to adopt the latter. 



§ 8. Snhclasses of Ilmmatocrya. — With the best insight — 

 peering into the dark vistas of the remote past — tliat one can 

 command into the nature of the strange forms which then 

 perished, and comljining with pala3ontological research the results 

 of anatomical and developmental scrutiny of existing vertebrates, 

 the following seem to be the best defined cold-blooded groups, 

 each with such characters in common as leads to their being called 

 ' natural,' and of a value which may be expressed l^y the term 

 ' sub-class.' 



I. Deemopteei. III. Plagiostomi. 



II. Teleostomi. IV. DirNoA. 



V. MONOPNOA. 



Subclass I. Deemopteei. — Body vermiform, limbless; endo- 

 skeleton membrano- cartilaginous and notocliordal,'^ ril^less ; skin 

 scaleless, lul)ricous ; a vertical fin-fold Ijordering the hind part of 

 the body, without fin-rays ; myelon opaline, ductile, elastic ; no 

 sympathetic nerve ; organ of smell single ; eyes wanting, or very 

 small ; ojDtic nerves not crossing each other ; auditory labyrinth 

 of one or two semicircular canals ; mouth jawless, or suctorial ; 

 alunentary canal straight, simple, without c;ecal appendages, 

 pancreas, or spleen. Branchial function independent of the mouth ; 

 heart, without ' bulbus arteriosus ; ' a pulsatile portal sinus ; no 

 swim-bladder ; testes and ovaria elongated plates without ducts ; 

 generative outlet peritoneal ; ova numerous, small, simultaneously 

 developed, and impregnated externally ; cleavage of yolk entire ; 

 no amnios or allantois ; a metamorjjhosis, as, e. g. from Ammo- 

 ccetes to Petronvjzon, after the third year from the egg. 



Subclass II, Teleostomi.'' — Body piscifonn, with medial and 



' Gr. haima, blood ; thennos. Lot. 



^ Gr. haima, blood; cruos, cold. 



' Retaining the notoehord or primitiTe basis of the vertebral column. 



■* This word (from Gr. telos, end or completion ; stoma, mouth ;) refers to the com- 

 pletion of the mouth by opposing upper and lower jaws, and also to its terminal 

 position, opening at the fore end of the head. 



