APPENDIX. 



707 



Fiff. 657 



St. Petersburg Academy, 18G9) also shows that the visceral 

 layer in the Libelhilid;e enters, together with the " amnion," 



into the formation of the yolk sac. 

 Melnikow remarks that '" it appears 

 from these facts tliat the differences 

 which we see in the embryonal mem- 

 ', ""■ branes of insects, are in direct rela- 

 tion to the mode in Avhich the prim- 

 itive band is formed. Tt seems, 

 therefore, that the mode of origin of 

 the primitive band, or its position in 

 relation to the yolk, is concerned in 

 tlie above mentioned differences of 

 the embryonal membranes. 



5J7 vT 



Development of the Louse. — 

 After the budding out of the limbs 

 from the primitive band, tlie germ 

 appears as seen in Fig. Go 7. We 

 now see the amnion {am) surround- 

 ing the yolk mass, and the visceral 

 membrane (db) within partially envel- 

 The head (r/i, procephalic lobes, or anten- 

 nal segment,) besides the antennae (o.s), bears thi-ee pairs of short 

 tubercles, which are the rudiments of the mandibles, maxillte, 

 and labium or second raaxilhe. Behind the mouth-parts arise 

 six long slender tubercles forming the rudimentary legs, while 

 the primitive streak rudely marks out the ventral walls of the 

 thorax and abdomen. Fig. 058 represents the head and mouth- 

 parts of the embryo of the same louse ; vk is the forehead, or 

 clypeus ; ant, the antenuiie ; mad, the mandibles ; max\ the first 

 pair of raaxillse, and max-, the second pair of maxillae, or 

 labium. Fig. 659 represents the mouth-parts of the same 

 insect a little farther advanced, with the jaws and lal)ium 

 elongated and closely folded together. Fig. 6G0 represents the 

 same still farther advanced ; the mandibles are sharp, and 

 resemble the jaws of the Mallophaga or ])iting lice ; and the 

 maxillae (viax^) and lal)ium {mu.ir) are still large, while after- 

 wards the labium becomes nearly obsolete. Fig. GGl repre- 



Embryo of louse. 



oping the embryo. 



