July i, 1921 
Larval Stages of H. bovis and H. lineatum 
441 
ing. Riley found that this young or first-stage larva was armed 
heavily with spines and was wholly unlike the much longer, apparently 
unarmed larva found by Curtice in the esophageal walls or by Hin- 
richsen in the spinal cavity. Riley states that— 
In the absence of any knowledge of an intermediate form, the larva found in 
the esophagus may be considered as the second stage 
and designates the two stages found by Brauer as the third and fourth 
stages. In 1914, Glaser (5, zo), of Germany, and Carpenter, 
Hewitt, and Reddin (2), of Ireland, first observed the first-stage larva 
of H. bovis outside of the egg. The three last-named investigators 
give a complete illustration of the first-stage larva as it appears after 
emergence from the eggshell. 
So far the four larval stages mentioned above have been the only 
ones known, but during recent studies by the writer for the purpose of 
determining distinguishing characters of all the larval stages of both 
species the fact was revealed that there is another stage to be found 
in the esophagus of the host. This new stage is unlike the small, 
heavily armed larva that hatches from the egg or the larger, spineless 
larva that is later found in the esophagus or on the back before molting 
to the next spiny stage, formerly known as the third stage. Careful 
examinations were made of a large series of larvae of all sizes measuring 
up to 14 mm. in length taken from esophagi and others measuring as 
high as 16 mm. extracted from the backs of cattle shortly after the 
hole through the hide had been completed but before the molt to the 
next larger or spiny stage had taken place. These studies conclusively 
revealed that the smaller larvae in the esophagus are not of the same 
stage as some of the large larvae measuring from 11 to about 14 mm. in 
the esophagus and all of those that later appear in the subcutaneous 
tissues of the back. Since the smaller armed larva found in the esophagus 
differs from the first stage hatching from the egg it must be considered 
the second stage, the large, spineless larva in the esophagus and in the 
back the third stage, and the following two armed stages as the fourth 
and fifth. There still remains, of course, the possibility of the occurrence 
of other intermediate stages, especially between the first stage and the 
first one found in the esophagus. The third or unarmed stage that 
reaches the back molts from the smaller or armed second stage before 
it leaves the esophagus, or possibly, in some instances at least, on its 
journey to the back. Many specimens from gullets as long as 14 mm. 
are still in the second stage while others similarly located and measuring 
as low as 11 mm. are in the third stage. The early investigators over¬ 
looked the unarmed stage in the back and concluded that there were 
only two stages encysted under the skin. This oversight was probably 
due to the fact that at the time the unarmed larva has punctured the 
hide and is undergoing the molt to the next stage the swelling or the 
