June 15, 1914 
Citrus-Root Nematode 
221 
larvae of the form shown in figures 6 and 7. The movements of these 
larvae are slow and weak, and yet the young 
stages, especially those of the female, are 
more active than those of the adult. At no 
stage of its existence are the movements of 
Tylenchulus semipenetrans anything but rela¬ 
tively slow and weak, and it is altogether 
improbable that through its own muscular 
exertions it ever migrates any great distance. 
Once the head of the female becomes well 
embedded in a Citrus root, in the manner 
shown in figure 8, c, it is practically impossi¬ 
ble for her to retreat. She therefore be¬ 
comes fixed for life and dies at the point 
where this entrance was made. “ Shells, ” 
or empty skins, of dead females are not in¬ 
frequently found on infested roots. Figure 
8, c, shows a female that has partly pene¬ 
trated a Citrus root., It will be seen that at 
the surface of the root the body is con¬ 
stricted, both the portion inside and that 
outside having a much greater diameter 
(see also fig. 9). It is the swollen character 
of the anterior portion of the embedded 
female that prevents retreat. As she grows 
older and increases in size, her head pene¬ 
trates farther and farther, but never so far 
as to be out of harmony with the specific 
name “semipenetrans ” By the use of her 
strongly developed oral spear, the tissues of 
the roots are punctured, and the food, con¬ 
sisting of the sap and protoplasmic matter 
of the root, is ingested. 
The females of Tylenchulus semipenetrans 
sometimes appear to be somewhat gregar¬ 
ious; at least it is not uncommon to find 
the adult females arranged in rather defi¬ 
nite groups on the roots. The cause of this 
phenomenon is not yet understood but may, 
perhaps, arise in this way: Larvae from the 
same batch of eggs in searching for food 
naturally seek the nearest suitable root. 
The mother worms, having injured or 
killed the root in their immediate vicinity and the root having accord- 
Fig. 5.— Tylenchulus semipenetrans: Fe¬ 
male ready for fertilization. Note the 
increased size of the excretory pore,», 
as compared with previous stages; 
see figures 7 and 12. The pore is lo¬ 
cated farther back than in any other 
known species of nematode, a , Lip 
region; b, guide of spear; c, shaft of 
spear; d , lumen of oesophagus; e, 
median oesophageal bulb;/, nerve 
ring; g, cardiac oesophageal bulb; h, 
beginning of intestine; o', ovary; n\ 
duct of renette; n, excretory pore; r , 
vulva; s, wings of the cuticle; V, de¬ 
teriorated anus; i, terminus. 
