Miss Agnes Crane — Evolution of the Brachiopoda. 69 



mentary, the liver large, and the digestive canal has a terminal 

 orifice, lateral in Lingula, dorsal to the median line in the anomalous 

 Crania. The hingeless Brachiopoda are heartless creatures, and 

 the circulation of the colourless lymph is efi"ected by ciliary action. 

 This group was named Lyopomata, or " loose valves," by Owen ; 

 Inarticulata, by Huxley ; and King's name of Tretenterata indicates 

 the important physiological distinction (48). 



The Arthropomata, Articulata, and CHstenterata, on the other hand, 

 are characterized — as their respective names imply — by jointed valves 

 or articulated, essentially calcareous shells, with hinged valves united 

 by interlocking hinge-teeth fitting into sockets in the opposite valve 

 and in the majority by the absence of a visceral foramen. The 

 cartilaginous arms are supported either by short bands or crura, by 

 calcified loops, or spiral frameworks. The more highly developed 

 members of the hinged sub-class have a lymphatic heart and supple- 

 mentary vesicles [Magellania venosa), and a true vascular system. 

 But accessory hearts are not uncommon in the animal kingdom. 

 There is one situated, for instance, in the tail of the eel, which, 

 perhaps, accounts for its extreme liveliness. In all the surviving 

 species of this articulated sub-class the digestive tube terminates in 

 a coecum. Evolution does not always imply progress, however, and 

 this is one instance of the origin of a sub-class through degeneration. 



This peculiar physiological feature — a reversion to the simpler 

 digestive process of the sea-anemone — is not predicable of the earliest 

 fossil articulated Brachiopoda; for in some species of the pro- 

 trematous and telotrematous orders the visceral foramen was retained. 

 This visceral foramen was pi'esent in Alhyris, Bensselloeria, and 

 Cryptonella, i.e. in members of the spire-bearing and Terebratuloid 

 stocks at the earliest epoch of their derivation from the antecedent 

 Protremata. Its closure was concui'rently evolved no doubt with 

 the gradual development of the interlocking hinged shell and sub- 

 sequent growth of the shell-plates which ultimately covered in the 

 deltidial area of the unibonal region. The change originated in 

 that order Protremata, so prolific in short ranging genera. Is it 

 unreasonable to assume that the period of this great functional 

 derangement, a physiological crisis in the history of the develop- 

 ment of the race, exercised an unfavourable influence on the vitality 

 of the first articulated order in which it originated ? It is a certain 

 fact that only one genus out of more than eighty which have been 

 referred to this order of Protremata have survived to the present 

 day. The majority enjoyed but a comparatively short range in 

 time ; the sole survivor is LacazeUa Mediterranea, characteristic of 

 the secondary family of Thecididm, and I am inclined to ascribe 

 the persistence of this genus to the extraordinary development of 

 internal calcareous spicula which permeate the mantle and form 

 a protective covering to all the vital organs of the little animal 

 inhabiting the shell — an absolutely unique feature among the 

 Brachiopoda. 



The class in general has otherwise progressed during evolution 

 by expansion of the anterior elements of the body, development of 



