418 LECTURE XVIII. 



there is no room for more ova, or not food enough for such when 

 hatched. After the ichneumon has deposited the ova, she plasters 

 over the wound with the colleterial secretion. 



In the insects of the genus Cynips, which are nearly allied to the 

 ichneumons, the female has an ovipositor very similarly modified ; their 

 place for oviposition is the leaves of trees ; and the ova excite an 

 action in the cellular tissue of the leaf, which results in the formation 

 of a warm and nutritious bed for the larvae. The products called 

 " nut-galls " result from such a procedure of the Cynips Querci. 

 In an insect allied to Aphis, the Chermes, or Psylla abietis, the last 

 act of the oviparous female, at the close of summer, is to deposit her 

 ova in the rudimentary leaves of the fir-tree ; when these leaves, 

 instead of growing to the length of the others, become thickened, and 

 are converted, by t^ie irritation of the ova of the Chermes, into a 

 series of cells of a compact structure. In the Hunterian preparation 

 (No. 2972) a section has been removed, showing the cavities con- 

 taining the larvae. In another preparation (No. 2975) is a specimen 

 of the article in the old Materia Medica, called " Bedeguar." It is a 

 twig of the common wild rose, from the end of which a tuft of mossy 

 fibres has shot out, in consequence of the irritation induced by the 

 presence of the ova and larvce of the Cynips Hoses. Hunter has 

 made a section of this monstrous growth, exposing several of the 

 nidaraental cavities and their small white larvae. 



In the gad-fly (CEstrus bovis) the ovipositor is like a telescope, 

 terminated by boring instruments ; by means of these the integument 

 of the ox is perforated, and the egg is then deposited underneath the 

 skin ; a peculiar kind of inflammation is set up, followed by hyper- 

 trophy and condensation of the cellular tissue, and in the nidus thus 

 produced the larvae are developed. In the Bot-cestrus ( Gasterophi- 

 lus equi) the ova are destined to be incubated in the alimentary canal 

 of the horse ; and one might wonder how their passage could 

 be insured into such a locality. The instinct of the female impels 

 her to attach the ova to the hair of those parts of the body which is 

 most readily reached by the horse's lips or tongue ; the ii'ritation 

 of the attached ova excites the action, and so they are picked or 

 licked off and swallowed. 



Many insects deposit their eggs in the earth, and the females of 

 such are provided with instruments for digging. In the preparations 

 of the Locust (No. 3166 & 3168), they are seen to consist of two hard 

 elongated valves ; these, in close juxtaposition, are thrust into the 

 earth, like the gardener's dibble ; the valves are then separated by 

 muscles, and the eggs are protruded along the interspace and depo- 

 sited like seeds in the ground. The analogous part in the bee is that 



