748 PROCEEDINGS OF THE ACADEMY OF [Oct., 



slightly thickened margins. The third row of spicules (Sp. 3) is com- 

 posed of a circle of needle-hke spines, seven in number: one dorsal, 

 one pair of dorso-lateral, one pair of dorso-ventral, and one pair of 

 closely approximated ventral spicules. All these spicules project 

 backward when the armature is evaginated. The three stilets point 

 forward; one of them is ventral {St.v., figs. 33-35), and the others 

 ''fi'^Tso-lateral (St.d.). Each is a slender rod, with the proximal end 

 widfe^Aed, but with a depression on each side of the expansion (there 

 shapecl ^ike a human red blood corpuscle) ; and with the distal end also 

 expanded and bearing on its median surface a series of fine parallel 

 ridges. The stilets surround a delicate canal, at the base of which 

 opens the duct of the gland {Gl.d.). The whole armature is an exqui- 

 site device for the penetration of the tissues of the host, and for moving 

 through them — the stilets penetrating, the spicules by their gripping 

 pidiiVig the larva forward. One does not know which to admire more, 

 %ke perfection of the larva for occasioning torture or the beneficence 

 of the Providence allowing such torment. 



The axis of the proboscis is separated from the outer wall by a space, 

 archico?!, and is composed of a cord of cells extending from the base of 

 the stilets to the diaphragm (figs. 36, 37). That part of this cord 

 nearest the stilets passes over continuously into the hypodermis, and 

 is composed of a mass of cells without perceptible boundaries, contain- 

 ing a number of large nuclei. So far as I can determine these are sim- 

 ply undifferentiated ectodermic cells. The other end of the cord is 

 made up of a numl:)er of long spindle-shaped cells (Fib.), attached at 

 one end to the diaphragm ; these may serve as elastic retractors of the 

 evaginated armature. 



The musculature of the proboscis is composed exclusively of longi- 

 tudinal fil^res (Mus. of figs. 36 and 37), the only faintly shaded struc- 

 tures in these drawings of the proboscis. These muscle cells are too 

 minute for any determination of their finer structure ; one can simply 

 determine their long spindle shapes, the presence of nuclei in them, and 

 the fact that they do not form a continuous layer, but are separated 

 from one another though parallel. Their arrangement is shown in figs. 

 36 and 37. 



All this region anterior to the diaphragm has been called by me the 

 proboscis, because evidently the whole is simply an organ for penetra- 

 tion and locomotion in the host, even though it composes about one- 

 half of the body. There is no entoderm in its constitution (except 

 the duct of the gland body situated behind the diaphragm), and mesen- 

 chvm onlv in the form of the musculature; all the remainder is ectoder- 



