44 



however, not sexually mature ; three moults occur, in about 

 14 days its growth is complete, and the insect is sexually 

 mature. The females lay 100-200 eggs. Lice, especially 

 when young, are delicate creatures. They are voracious 

 feeders, and must be fed at frequent intervals. They, as a 

 rule, are unable to withstand starvation for more than two 

 days. They are very sensitive to heat and drying, and soon 

 succumb at temperatures above 25 C. , unless the air be 

 Kept nearly saturated with moisture. They live in clothing 

 and bedding, and feed several times in the 24 hours if oppor- 

 tunity be given. The optimum condition for their develop- 

 ment occurs in the case of those persons who seldom wash 

 their clothing or change it for sleeping:. 



.The general arrangement of the alimentary canal may be 

 seen in Fig. 16, which also shows the sac in the floor of the 

 mouth which contains the piercing organ. The four salivary 

 ducts (two only of which are shown) open into the base of 

 this sac. The pharynx is a chitinous organ which collapses 

 by its elasticity, and suction is produced by the contraction 

 of the muscles (m.) attached to its dorsal surface and the 

 chitinous skeleton of the cranium. The blood is forced into 

 the stomach by the relaxation in order of these muscles from 

 before backwards. The stomach or crop is a capacious 

 organ with two lateral diverticula from its anterior end. 



The body louse obtains its nourishment entirely by sucking 

 blood. It is provided with penetrating instruments, the 

 apposition of which forms a canal through which the blood is 

 pumped into the stomach by a pharyngeal pump similar to that 

 of the flea. These piercing instruments are not permanently 

 exterior to the head and carried tucked away in a labiurn 

 as in fleas and bugs, but, as described by Pawlovsky (1906), 

 the apparatus is retractile and contained in a special pocket 

 in the floor of the mouth, Fig. 16. The anterior part 

 of the mouth is provided with a ring of booklets, which 

 is everted when the pricker is thrust out. (Fig. 17, B, A.) 

 When the insect feeds the tubular "pricker" (p.} is pro- 

 truded through the mouth and penetrates the skin of the 

 host, and the booklets serve to attach the mouth to the skin. 



The exact way in which the sucking tube is built up is not 

 quite clear, but from preparations made by my colleagues, 

 Mr. Bacot and Dr. Eowland, 6 the arrangement of these parts 

 appears to be as follows. Three elements enter into the 

 formation of the "pricker," each of which is bifurcated at 

 its base (see Fig. 17, A and B). From the dorsal and ventral 

 aspects of two of these parts, just anterior to their bifur- 



6 I am greatly indebted to Mr. [Bacot and Dr. Rowland, not only for 

 lending me specimens of the mouth parts of the louse, but also for their 

 kindness in making fresh dissections for the purpose of this lecture. 

 The mechanism of the sucking apparatus of the louse is much more diffi- 

 cult to comprehend than that of the flea or bug, and the description 

 given merely represents the conclusions I have been able to arrive at 

 without a prolonged study of the intricate arrangement of the organ 



