174 MR. A. E. CAMERO^f ON 



diminish so tliat the dominant female, in order to safeguard the 

 species against utter extii'pation, began to i-eproduce pai^theno- 

 genetically. We must understand that the process has been a 

 very gradual one, proceeding sIoAvJy throughout several centuries, 

 the male finally becoming ahuost extinct. 



Another interesting question intimately connected with the 

 subject of parthenogenesis may be asked. Why does the female 

 produce ova from which only females arise ? While I ofi'er no 

 suggestion, I may be permitted to allude to the same phenomenon 

 Avhich occurs regularly in many of the Cynipidfe or Gall-flies. 

 The male of Gynlps hollari, the maker of the marble-gall of the 

 oak, has never been observed, although many entomologists have 

 given this species their close attention, and it is now generally 

 believed that it does not exist, but that parthenogenetic repro- 

 duction is the only method of pi^eserving the species. 



The following is quoted from Adler and Straton's ' Alternating 

 Generations' (Oxford. 1894). 



" It would appear that in Cynips kollarl the sexual generation 

 is wholly subordinated to the asexual, and in EJwdites rosce, which 

 forms the pretty Bedeguar galls on the rose-tree, the process is still 

 going on, and the males are becoming functionless and extinct. 

 ... It is difficult to believe that the agamous (or asexual) can be the 

 primitive form ; or that the perfectly foi'med sexual organs could 

 have been evolved unless the sexual had been the earlier 

 generation." 



Alimentary Canal. 



While at the Royal College of Science, London, in the beginning 

 of 1911, it Avas suggested to me that the alimentary canal of 

 Bacillus rossii would repay carefvd observation. The material at 

 hand I subsequently worked up in the Zoological Depaitment 

 of Manchester University, and I here take the opportunity of 

 expressing my indebtedness to Professor Hickson as well as to 

 Mr. Mangan 'for many timely hints. 



In the Orthoptera viewed as a whole the alimentary canal 

 shows a very uniform structure ; but in the various families 

 there are many secondary differences, sometimes even in the same 

 family, necessitating specird description. The gizzard is im- 

 portant in the Orthoptera, and there are diverse degrees of 

 complication in its chitinous armour. The intestinal c?eca vary 

 greatly in number, there being eight in Mantida; and Blattidse, 

 six in Acridiidfe, and one pair of lateral CEeca in Locusticlfe and 

 Gryllidfie. The diverse variations of structure in the gizzard, 

 its different degrees of complexity added especially to the pre- 

 sence or absence of intestinal creca, suggested to Bordas (1897) a 

 method of dividing the Orthoptera into two large groups : 



1. The Acolotasia, or Orthoptera without intestinal ca3ca. ; 



2. The Colotasia, or Orthoptera wdth intestinal creca more or 



less numerous. 



