80 



ACCOUNT OF THE PHASMIDAE, WITH NOTES ON THE EGGS. 



demonstrate a continuity between the two parts at an earlier stage. The operculum 

 it should be remembered is not seated on the chorion, but the latter is (apparently) 

 quite absent from the anterior pole of the egg, where it is replaced functionally (as 

 a covering and protecting body) by the operculum. Tn a comparatively early stage 

 of the egg-growth, before there is any exochorion so that only the membranous 

 endochorion is present, the operculum may be demonstrated as an independent 

 structure placed on the yolk, and enclosing a smaller body of yolk. The egg itself 

 may, at this stage, be entirely emptied of its yolk without affecting the opercular mass 

 of yolk (Fig. 38). The exochorion of the operculum is formed subsequently, just as 

 the exochorion of the capsule is formed subsequently, but there is no union between 

 the two. The manner in which the operculum is formed is obscure ; two methods may 

 be suggested; 1, autotomy of the pole of the egg; 2, adhesion of the mass of matter 

 from the adjacent nutrient chamber, to form as it were a very imperfect second egg. 

 On this latter view the egg and operculum may be considered as the equivalent of 

 an egg and a mass of matter added from another egg-chamber, and in that case 

 when a capitulum is also present the egg would consist of egg-proper + opercular mass 

 of nutrient matter + capitular mass of nutrient matter 1 . 



The fact that the vitelline membrane is thicker about the opercular area where 

 the chorion is absent suggests that the missing part of the latter may possibly 

 be added to the former, and thus account for the thickness. But on the other hand 

 it is quite probable that the extra thickness may arise in course of the process of 

 autotomy, if that be the method by w T hich the operculum is formed. 



The egg of a Phasmid, provided as it is with a separate and perfectly fitting 

 operculum, is a very remarkable object. Hitherto it has appeared to me very difficult 

 to imagine how it could have been produced by a gradual process of evolution. From 

 the imperfect study I have now made T think it probable that the Phasmid egg will 

 be found to consist of an egg proper and of one or two imperfect eggs mechanically 

 coadapted by pressure arising from the enormous distention of the egg-tube. It appears 

 to me reasonable to suppose that it might have been thus produced in a gradual 

 manner in the course of time. 



The observations on the spirit specimens may be thus summarised : 



1. The ovarian tube contains nutrient matter divided segmentally into separate 

 masses, and the lower part of the tube is constricted so as to form chambers in 

 each of which there is a mass of nutrient matter. 



2. The mass of matter in the lower chamber grows enormously so as to cause 

 extreme distension of the egg-tube, and the whole mass of matter in the chamber 

 (or very nearly the whole) is found to be covered with two membranes (endochorion 

 and oolemn), the outer one of which is deficient at one pole of the egg where 

 the (as yet membranous) operculum is situate. 



3. The exochorion accumulates between the wall of the egg-tube and the outer 



1 I think it probable that some other curious forms of Insect-eggs (e.g. those of Cynipidae and some 

 Hemiptera Hrteroptera) may prove to be compound eggs of this nature ; that is to say, formed by the com- 

 bination of the more or less separate growths of more than one egg-chamber. 



