360 



THE POPULAR EDUCATOR. 



which are far inferior to the Conchifera, and bear a stronger 

 relation to the Tunicata and Polyzoa than they do to the other 

 class, which will come under our notice in the after-part of the 

 lesson. 



Brachiopoda. These creatures are, for the most part, fixed to 

 the rocky bottom of the sea, either by a fleshy stalk, which 

 passes out from the body through a hole, a slit, or a passage in 

 the ventral valve, or else by having this under-valve fixed to its 

 support directly. In the first case the connection is organic, 

 r.nd the creature can move 

 itself upon its stalk by the 

 aid of muscles, which are 

 placed inside the shelly 

 box; and in the latter case 

 the connection is inor- 

 ganic, and the creature ia 

 entirely immovable. Tak- 

 ing the Waldheimia as a 

 type, because it is the 

 genus which has been best 

 studied, not only by Con- 

 tinental anatomists, but 

 also by Hancock, Huxley, 

 and Owen, we proceed to 

 describe its structure. The 

 reader should, however, be 

 warned that though this ia 

 a good typical Brachiopod, 

 all that will be said about 

 it does not apply to every 

 species of the class, and 

 that the structure has 

 been very differently in- 

 terpreted and explained by 

 the great naturalists above 

 named. 



The shells are best un- 

 derstood from the illustra- 

 tion. It will be observed 

 that the ventral shell is 

 ^ery concave and globose, 

 lodging the animal as in o. 

 cup, while the dorsal shell 

 is nearly flat, and acts as 

 a lid to the cup. The 

 ventral shell has a round 

 hole in one end through 

 which the stalk passes. 

 Between this hole and the 

 great opening of the shell 

 is a triangular space, and 

 at the angles at the base 

 of the triangle are two 

 little teeth. These teeth 

 fit into sockets in the flat 

 shell, which has also de- 

 veloped from it a large 

 calcareous loop. This loop 

 consists of two arms, 

 which run forward en 

 either side, and then, leav- 

 ing the shell, are turned 

 back to unite almost above 

 (or below, in the natural 

 position of the animal) the 



point from which they spring. When the two shells are placed to- 

 gether as when the animal occupies them, they look not unlike the 

 Eastern oil-lamps which are always represented as being carried 

 by the ten virgins in pictures of the parable ; the hole in the ventral 

 shell, of course, corresponding to that through which the wick 

 passes in the lamp. Hence, these shells have been called lamp- 

 shells. When the valves are united on the hinge as in life, this 

 hinge does not allow them to be parted from one another, except 

 for a short distance. The soft parts of the animal occupy a 

 very small par- of its hard box, being confined almost exclusively 

 to the part between the arms of the loop, and to about the one- 

 third of this space nearest the hinge. This restriction applies 

 to the visceral and muscular masses. There are, however, large 



and long extensions of the body stretching beyond this confined 

 space. Thus, two large vascular membranous sheets lino the 

 valves right up to the very edge of the shell, where they are 

 fringed with strong and numerous bristles. There are also two 

 long arms, which stretch away from the mouth on each side. 

 These are so long that, if unfolded, they would stretch beyond 

 the limits of the shell ; but they are supported by the calcareous 

 loop, and follow its bendings. These arms have a delicate fringe- 

 of little fingers, which arise all along their outer sides ; and 



these little fingers are 

 clothed with cilia, which 

 create currents of water 

 towards the mouth, and 

 thus the animal is fed. 

 The mouth has no hard 

 parts or jaws, but only 

 two lips, of which the arms 

 may be considered the 

 sidelong extensions. It 

 opens towards the gaping 

 part of the shells, and ateo 

 downward. The stomach 

 is rounded, and receives- 

 the passages from the liver 

 which surrounds it, aad 

 the intestine bends down- 

 ward and ends blindly be- 

 low. At the back and above- 

 the stomach ia the simple 

 saccular heart, which sends 

 off from each of its sides 

 two vessels, one of which 

 goes to the stomach and 

 viscera, and the other to- 

 the mantle lobes. These- 

 lobes of the mantle are so 

 well supplied with blood, 

 and the vessels are so large- 

 which traverse them, that 

 it is supposed that the 

 blood is there aerated, and 

 hence these creatures have 

 been called Palliobran- 

 chiata, or breathers by- 

 means of the mantle. 

 Bound the edge of each 

 lobe of the mantle which 

 lines the valves is a circu- 

 lar channel, and this first 

 receives the blood from 

 the heart, and from there 

 it passes back through the 

 more central parts of the- 

 lobes, being first conveyed 

 through fine vessels, aad,. 

 then collected into larger 

 and larger vessels until it 

 is returned by large sinuses 



BRACKIOPODA. I. WALDHEIMIA. H. DITTO, SIDE VIEW. III. DITTO, VENTRAL 

 VALVE. IV. DITTO, DORSAL VALVE. V DITTO, SHOWING THE MUSCULAR SYS- 

 TEM. VI. DITTO, TO SHOW ARRANGEMENT OP VISCERA. 



Befs. to Nos. in Figs. III. 1, aperture through which pedicel is passed ; 2, impres- 

 sion of capsular muscle ; 3, teeth of the hinge 4, impression of the adductor 

 muscles ; 5, impression of pedicel muscles ; 6, impression of cardinal (adductor) 

 muscles. IV. 3, posterior adductor and (3') anterior adductor impressions ; 7, 

 carbonate of lime loop to support the arms. V. 3, 3', adductors ; 4, pedicel 

 muscles ; 5, pedicel ; 6, cardinal and (8) ventral pedicel muscles ; 7, loop. VI. 

 1, mouth ; '2, stomach ; 3, intestine ; 4, anus ; 5, heart ; 6, entrance to pul- 

 satile vessel ; 7, adductor muscle ; 8, loop ; 9, arm-fringes. 



to the central parts. When 

 the blood has arrived at 

 these central parts, some 

 of it goes to supply them 

 directly, whilst the residue- 

 runs along the vessels of the 

 arms and the membranes 



connecting the arms, and so returns from them after having' 

 passed through the fine fringes. Thus it is probable that these 

 ciliated fringes of the arms are efficient, and perhaps the most: 

 efficient, instruments of aeration of the blood. After the return 

 from the arms and viscera, the blood on both sides of the body 

 is collected into a vessel which runs along above the stomach, 

 and then enters the heart again. 



Two organs, each with two compartments, and situated one 

 on each side of the body, have sometimes been considered as 

 hearts ; but they seem more probably to belong to the water- 

 vascular system, as they open externally to the animal, and 

 convey away the generative products. 



The nervous system of the animal is very simple ; the central 



