29 



fice, near but below that leading into the frontal sinus, which leads into 

 thesuperior maxillary sinus. (SeePlatell, a, b.) Abit of straw has been 

 inserted into theoriflce to show the place of openiag. From these places 

 the larvjB never emerge, but after maturing undergo calcareous degen- 

 eration. Those that arrive in the frontal sinuses seem to thrive, and at 

 the proper time are able to retreat through the orifice they first trav- 

 ersed and are finally sneezed to the ground. This history and the fig- 

 ures illustrating it, which have been drawn from nature, should satisfy 

 sheepmen who have thought that because the grubs were in the head 

 they must be in the brain. A glance at Plate III, with its three larvae 

 in the sinus (there were originally seven in the head which the artist 

 figured), will show that there is a bony partition, a, «, a, between the 

 brain and the larvjB. This is also the case in regard to those small larvae 

 which wander among the intricate windings of the upper turbinated 

 bone, g. The larvae of the (Estrus, or the grubs, never do and never can 

 penetrate into the brain. 



If one may judge from the black dots indicating a previous hemor- 

 rhage scattered over the mucous membrane, the irritation set up by the 

 wandering embryos is very considerable. In the sinuses of heads which 

 contain older embryos other changes are to be noticed. They are filled 

 with catarrhal matter which has been produced by the irritation of the 

 larvae, and the mucous membrane is greatly thickened. These changes 

 may also be observed over the turbinated bones, g, the greatest changes 

 occurring in the superior, the one next the brain. The membrane 

 which covers the latter is the one in which the nerves of the sense of 

 smell are distributed, and a thickening of the membrane must greatly 

 interfere with this sense. This is no small matter, for it is mainly by 

 this sense that the sheep separates its food from other herbage. 



In addition to the catarrhal product and thickening of the membrane, 

 it has been noticed that the membrane near the base of the turbinated 

 bone — near m — is sometimes very dark colored. At this point the 

 bone is exceedingly thin and pierced by a number of holes through 

 which the olfactory nerves, or nerves of the sense of smell, pass. It is 

 not unusual to find the membranes of the brain in the immediate vicin- 

 ity blackened by minute dots, indicating a previous inflammation at 

 this point. This affection of the membranes is probably caused by an 

 extension of the inflammatory process from the nasal cavity. 



When the larvre become entrapped in the maxillary sinus they ex- 

 cite the same catarrhal secretions and thickening of the membranes as 

 elsewhere, which finally fill the cavity, the outlet of which is at the top. 

 All this irritation is due to the insertion of the claws and scratchiugs 

 of the abdominal spines. The larvae live on the material in which they 

 move. They seem to obtain i^leuty of air even in the most crowded 

 recesses. They continually cover and uncover the breathing pores 

 (Plate I, Fig. 10a), and in so doing keep them cleaned of all foreign 



