160 



Agricultural Gazette. 



Fio. 8.— Larva of T. are- 



narius akter enter- 



iKo A Boot, x 100. 



8, spear ; b, median 



bulb ; V, ventral ^Innd 



which empties tlirougli 



the excretory pore p ; a, 



anus. 



are shown in the figures, and their structure has already been commented 

 upon. The larva makes its way to a rootlet, applies its mouth, and exerts a 

 powerful suction by means of the muscular median bulb, at the same time 

 thrusting forth its spear by means of appropriate muscles. The cells of the 

 epidermis of the rootlet are thus pierced, and are then sucked dry and made 

 to collapse. At the aperture thus made other and deeper cells are similarly 

 attacked. Continuing this lino of action, the worm makes its way into the 

 interior of the rootlet. At least, such I believe to be 

 the method of attack, although I must iidd that my 

 opinion is deduced from the structure of (ho organs of 

 the worm and the effects on the tissues of the plant. I 

 have not witnessed the actual entrance of a larva into 

 a rootlet. Once within the rootlet, the worm is in the 

 presence of an abundance of food, and begins to grow 

 apace. Here again it brings into play its piercing and 

 sucking apparatus. Its very existence depends upon 

 these organs, and their importance is attested by the fact 

 that throughout the life of the worm they remain in 

 perfect condition, although numerous other organs 

 become completely degenerate. By continually thrust- 

 ing forth the sharp spear the juicy cells of the rootlet 

 are pierced, and their contents are then sucked in. The 

 growth of the larvae consists in a rapid and great 

 increase in diameter, so that the originally slender worm 

 soon takes on the plump form shown in Fig. 3. The 

 tail and head alone retain somewhat of their original size and form. Even 

 the tail disappears at a later stage. 



Whether the change now to be described takes place at the first moult, I 

 cannot say. Eeasoning from the size of the larva, I should answer iu the 

 affirmative. It is certain that at an early stage, shown in Fig. 4, the worm 

 undergoes a change in which the tail disappears and, a])parently, the anus 



with it. Fig. 4 represents then, we 

 will say, the first or second moult. 

 The old skin is shown, and inside it 

 the larra. It is evident that the 

 result of this moult will be a tailless 

 worm. The porous excretorius and 

 the duct are also clearly shown in 

 the figure. The excretory appa- 

 ratus, therefore, persists, as does the 

 muscular system. That the struc- 

 ture of the spear and oesophagus 

 remain essentially unaltered is suffi- 

 ciently attested by Fig. 5, taken from 

 a worm of about the same size as 

 that shown in Fig. 4 ; there is no 

 alteration except that the whole 

 structure has increased in size, and, therefore, in effectiveness. 



Up to this time the sexes remain indistinguishable or nearly so, but 

 at this st.Tge the life-histories of the two sexes begin plainly to diverge, 

 and present, from a biological point of view, a most interesting series 

 of phenomena. Let us first cons-idcr the history of the female. Fig. 4 

 represents a female, the first clear indication of the sexual organs being 

 exnibited in the single coll at o. This cell, by dividing, soon gives rise to 



Fio. 4.— Moui/ri.vo Larva 

 op T. arenarius. x 100. 

 c, old skin ; s, spear ; v, 

 ventral f^Iand which emp. 

 tied through excrctorj* 

 pore p ; b, median hull) : 

 0, rudimentary se.xual 

 organ. 



Fig. 5, — Neck and Head 

 OK Fio. 3. x 200. 

 jr, spear; b, median 

 bulb ; p, excretory poro. 



