136 WHEELER. [Vol. VIII. 



sheaths of the ovipositor or sting, the development of the 

 innermost pair of blades is by no means so satisfactory. But 

 whether this pair is only a portion of the ninth pair of ap- 

 pendages, as most authors claim, or represents the tenth pair 

 of appendages, as I maintain, the main question at issue is 

 in no wise affected ; for it still remains true that the ovipositor 

 consists of two or three pairs of modified ambulatory limbs. 



In the male XipJiidiinn embryo it was claimed that the pair 

 of appendages on the ninth segment persists to form the defini- 

 tive styli ; those of the eighth and tenth segments disappear- 

 ing very early. The continuity of the styli with the embryonic 

 appendages was quite as satisfactorily observed as the con- 

 tinuity of the ovipositor blades. Cholodkowsky has made an 

 exactly similar observation on Blatta {'91^). The styli are, 

 therefore, the homologues of the second pair of gonapophyses. 

 Haase must therefore have gone astray in seeking to homo- 

 logize the styli with the styloid processes, or " Griffel," for 

 the styli are modified ambulatory appendages. Moreover, if 

 my interpretation is correct, he cannot have found, as he 

 claims, the evanescent rudiments of styli in young female 

 Blattids, since the second pair of "anal palps" are the homo- 

 logues of the styli {vide Huxley, '77). 



VII. The Subgesophageal Body in Xiphidium and Blatta. 



This structure, of which I have elsewhere ('92) given a brief 

 preliminary account, makes its appearance in the XipJiidimii 

 embryo, in a stage a little earlier than F. The somites in the 

 oral and thoracic segments are then established as closed sacs. 

 The stomodaeum is still a relatively shallow depression, and 

 the entoderm-bands starting from its inner end have made but 

 little progress. Sagittal (Fig. 61) and frontal sections (Fig. 

 62), through the heads of embryos in Stage F, show several 

 interesting details. A pair of somites (coe) lie in the mandi- 

 bular segment, and previous to this stage there was also a pair 

 of small somites with indistinct cavities in the tritocerebral 

 segment (tc). The planes of section in the two figures are 

 such that the deutocerebral somites are not shown. A mass 



