﻿THE CATTLE GEUBS OR OX WAEBLES 45 



occurs it is probably due to the fact that the lower eggs, being 

 closer to the skin, are kept at a slightly higher temperature. 



Several hours before hatching, the segmentation and rows of 

 spines are distinctly discernible through the shell. The larva be- 

 comes active shortly before hatching and can be obserA^ed through 

 the eggshell pressing the mouth parts forward against the end of 

 the egg. Finally the suture across the end of the egg is ruptured 

 and the larva crawls out rather rapidly. 



LARVAL ACTION AFTER HATCHING 



The larva of H. lineatiim after hatching usually crawls directly 

 down the hair which bears the egg and after feeling about with the 

 mouth parts begins to burrow directly into the skin at the base of 

 the hair. The body is usually more or less extended along the hair, 

 and during the initial efforts there is considerable twisting, expan- 

 sion, and contraction. After the first few segments have been 

 worked into the skin the larva becomes more quiet. The burrow- 

 ing is slow but usually rather steady in case of vigorous specimens. 

 Progress is retarded as the middle body segments reach the surface 

 of the skin, and usually it is slightly accelerated when the larva 

 has become almost completely imbedded. The time occupied for 

 a larva to disappear after it has begun burrowing has been ob- 

 served to be about one and one-half hours and sometimes consider- 

 ably longer. 



In nature it appears that several larvse frequently enter the host 

 through the same hole, and this no doubt greatly facilitates the pene- 

 tration after the first larva has gained entrance, 



Considerable difficulty was experienced in watching the penetra- 

 tion of the larvse into the skin, mainly owing to the difficulty of 

 holdins: a host quiet for considerable periods of time but also to the 

 fact that the larvse, on account of their small size and delicate struc- 

 ture, are very easily lost sight of. Most of the writers' observations 

 on penetration were made with freshly hatched larvae taken from an 

 incubator. Ea'cu with the most careful handling there was a high 

 mortality, apparently much gi-eater than when the eggs are attached 

 to the host in the natural way. It was observed^ repeatedly that 

 larva^ removed from an incubator and placed on hair would wander 

 about for a time before attempting to burrow and in so doing it 

 seemed that they became more sensitive to drying, probably through 

 the rubbing off" of the gelatinous material with which their bodies 

 are covered when they first emerge from the egg. Many larva? put 

 on hosts in this manner began l)urrowing, but perished during the 

 process. In making observations a calf was usually placed on a 

 taljle and finiilv held or even strajjped down so that the actions of 

 tlie larvae could' Ik; followed under hand lenses or binoculars. Where 

 the hair had been rlipjx'd closely, early tests with the penetration 

 of larva' through the skin were unsuccessful, and all sul)sequent 

 observations on penetration were made on hair one-fourth incli long 

 oi- longer. In order to reduce the fhances of escar)e withoul detection, 

 it was the usual |)ra<;ticc to clip closely or shave a narrow areii nronrid 

 a tuft of hail- and to place the hirva- upon this tuft. 



Several attempts were niiidc lo ol).serv(', the penetration ol liirva^ 

 on the hands or arms of man. Usually the lar\'uj were watched 



