THE OOTHECvE OF THE BLATTID.E. 



285 



the apex of the abdomen until the embryos are just about ready to 

 emerge, when it is deposited in a casual manner anywhere. It is 

 obvious that this type of ootheca is not derived from the chitinous 

 type but is merely an advanced development of the thin membrane 

 surrounding the egg-masses of Fancatliia, Pancldora, etc. 



Now, which is the more primitive habit in the Blattidae, viviparity 

 or the ootheca-forming habit ? This is a problem which cannot be 

 solved with certainty, but I believe that viviparity has in this family 

 a two-fold origin. In Blahera and Kiister/asta it is secondarily derived 

 from the ootheca-forming habit, as shown by the presence of a more 

 or less junctionless ootheca in these genera ; in Blattella it may well 

 be derived from an ancestral type, which deposited an egg-mass at the 

 beginning of the embryonic period. The Blattine ootheca, elaborate as 

 it is in structure, can hardly be regarded as truly primitive, and the 

 fact that it attains its highest development in the Nyctibnrinae and 

 lUattinae, two highly evolved subfamilies, is further confirmation of 

 the opinion that this structure came into being at a period com- 

 paratively late in the cockroach genealogical histoi-y. The following 

 diagram may make matters a little more clear. 

 Viviparous 



species, no q 

 ootheca. I 

 e.g., Fan- \ 

 chlora. 



Length of embryonic 

 period spent inside 

 brood-sac gradually 

 prolonged. 



Blattella-ty^^e of 

 I ootheca. Ovo- 

 I viviparous species. 



Viviparous species. 



Ootheca formed, but 



I retained in brood-sac 



; and f unctionless. 



e.g., Blahera. 







Blatta -type of 

 ootheca. 



Hypothetical ancestor 



depositing eggs singly 



or in egg-masses. 



Whether there is a grain of truth in this diagram or not, one thing 

 is clear and that is, that the various adaptations of habit and oothecal 

 structure are designed with the object of securing protection from the 

 attacks of external parasites. The appearance of these enemies 

 would soon render the position of unprotected eggs untenable and two 

 methods of protection could be adopted, either the eggs must be 

 retained inside the mother as long as possible, or they must be 

 concealed in a horny chitinous covering ; both methods have met with 

 success, but of the two the former seems to be the more successful, 

 seeing that the lllabera type of viviparity is secondarily derived from 

 the habit of forming a true and functional ootheca, and presumably is 

 so derived because of its greater value to the species. 



It only remains to give now a list of the sub-families and genera 

 in which the egg-laying habit is known. The Blattidae are divided 

 into sub-families, and the egg-laying habits are known in a certain 

 proportion of genera in each sub-family, except the Peiisphaeriinae 

 concernmg which we are almost quite ignorant. The following are 

 the sub-families and genera about which we have some information : — 



