376 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1925 



Fig. 1. — Various forms of insect eggs (all itiucli enlarged, but not to same scale) 

 A, egg of a housefly ; li, stnlki'd eggs of a lacewing fly, the goKien-eye, attached 

 to under surface of a leaf; C, egg of a cabbage butterfly; D, flat, overlapping egg^ 

 of a leaf-roller moth; E, eggs of potato beetle on under surface of a leaf; F, egg of 

 the snowy treo-criclcet inserted into an apple Iwig. 



in the stems of plants, or in the bodies of other insects. Eggs such 

 as the latter, including the eggs of grasshoppers, beetles, flies, are 

 iisiiall3' of a long-oval form, slightly curved, 

 and a trifle smaller at one end than at the 

 other. An egg of this kind will be the most 

 convenient to take as a type for studv (fig. 1, F, 

 fig 2). 



The external covering of the insect egg is 

 called the citorion (fig. 2, Gho). It is composed 

 of a tough, flexible substance, quite unlike the 

 Ijrittle shell of a bird's e^g^ deposited upon the 

 fcrg from the wall of the egg tube. The young 

 insect when ready to hatch either splits the egg 

 shell or gnaws a hole in it large enough to 

 allow it to emerge. An example of the first 

 method of emergence was given in the descrip- 

 tion of the hatching of a young cicada in the 

 Smithsonian Report for 1919, page 407, and 

 an example of the second method in the hatch- 

 ing of a young cankerworm described in the 

 Smithsonian Eeport for 1924, page 384. 



The newly laid egg appears to contain noth- 

 ing but a clear, watery, or creamy liquid, but 

 when examined under the microscojie in speci- 

 mens prepared and stained for microscopic 

 study, the interior of the egg is seen to have a 

 complex organization. Its fundamental substance is protoplasm, 

 but most of its bulk consists of yolk materials (fig. 2, Y) that 

 are mixed with the protoplasm. The protoplasm itself is visible 

 principally as a thin layer at the surface of the egg {CL) ; 



Fig. 2. — Section of a 

 typical insect egg, 

 showing its internal 

 structure 

 Cho, chorion, or 

 outer shell ; CL, cor- 

 tical layer of proto- 

 plasm ; Mic, micro- 

 pyle ; Vm, Nucleus ; 

 Vit, vitelline mem- 

 brane ; Y, yolk. 



