398 



THE YOUNG NATURALIST. 



fluid, which is so attractive to all insects, 

 whose visits are also of service to the plant 

 itself. In the Yellow Toad-flax (Linaria 

 vulgaris J which is common by the borders of 

 sandy fields and roadsides, and is known to 

 all school children as "Butter and eggs," 

 the spur is much larger, and it is also subject 

 to an abnormal development whereby five 

 spurs are formed on each flower instead of 

 only one. It is worth looking for. not only 

 as a curiosity, but as an aid to forming a clear 

 conception as to how the corolla apparently 

 formed of one petal is built up of several 

 united ones. The seed-vessels are perfectly 

 round, and tipped with the persistent hair- 

 like style, clasped by the five green sepals, 

 they look like large solitaire pearls in eagle's- 

 claw setting. The numerous little black 

 seeds are most curiously corrugated or 

 wrinkled, seen under a common lens they 

 have the appearance of being covered with 

 convoluted folds, this provision is useful in 

 preventing them, from rolling out of the little 

 chinks in which they are deposited, which 

 would be apt to occur if they were smooth. 

 The amazing fecundity of this plant has given 

 rise to one of its most popular common 

 names, "Mother of thousands ;" this would 

 also be applicable to its free flowering habit 

 as i: continues in bloom from May till 

 November. Although it is not a native of 

 Britain it is now thoroughly naturalised and 

 firmly established in many localities on old 

 walls and ruins, and no one would like to see 

 the little intruder e cpellei, exen if its eradica- 

 tion were possible, for it is harmless and 

 beautiful, and often adds a charm to other- 

 wise unsightly objects, hiding with its delicate 

 tracery the evidences of man's neglect or 

 decay. The generic name Linaria (Linwn, 

 liax) is given from the leaves of several 

 species resembling the leaves of flax, and the 

 common name " Toad-flax " has doubtless 

 arisen from its being a worthless or useless 

 plant, being destitute of the properties of true 

 llax, in the same way as many species of 

 Fungi are called "Toad-stools" to distinguish 



I them from true mushrooms. The specific 

 ! name Cymb.ilaria was bestowed on it from the 

 round leaves somewhat resembling cymbals. 



CONCHOLOGY. 



! LAX D AND FRESH-WATER SHELLS 

 By H. T. Robson, Stockton-on-Tees. 



The shells of Bivalves are formed of two 

 ; separate parts hinged together, each of these 

 | parts is called a Valve, and when the Shell is 

 spoken of both the valves are included ; the 

 ! Cockle, Muscle, and Oyster are familiar 

 examples of Bivalves. In some shells the 

 valves are equal, both being alike in size and 

 : shape; the Cockle and Muscle are examples 

 ' of these; in others they are unequal, the size 

 i and shape of the valves being different, of 

 I these the Oyster is an example. The two 

 I valves are spoken of as the Right Valve and 

 the Left Valve, according to their position to 

 the right or left of the animal as it moves 

 I itself along. The growth of the valves is by 

 : concentric rings around the margins, each 

 ! ring is not however of the same width all 

 ! round, but as in the Univalves, is wider at 

 : one part than another, giving the valves an 

 j oblique and rounded form ; the nucleus from 

 j which the growth proceeds, and which cor! 

 responds to the apex of the spire in a Uni- 

 valve, is named the Umbo, and forms a 

 rounded or angular projection at the back or 

 Dorsal margin of the valve ; the edge of the 

 ' valve opposite to the dorsai margin is called 

 i the Ventral margin ; the two sides or ends are 

 named the Anterior and the Posterior; the 

 Anterior side being that which is in front 

 when the animal is in motion, and the Pos- 

 ter. 'or behind. The Hinge is on the dorsal 

 ma.-gin, and includes various parts not, 

 necessarily all present in any one species ; 

 these parts are, the Teeth, consisting of pro- 

 jections and hollows on the inner surface of 

 the dorsal mirgin, with corresponding re- 

 cesses and projections on the opposite valve, 

 by means of which the two are fitted and 



