Nos. 455-456.] 



HEAD OF BLATTA. 



789 



In the face of these opinions it may seem somewhat venture- 

 some to assert that in Blatta there are evidences of the presence 

 of such appendages. And yet, I beUeve that the facts warrant 

 this conchision. In embryos of the eleventh day, in favorable 

 specimens there are to be seen between the antennal and the 

 mandibular rudiments, in the region occupied b)' the trilocerebral 

 ganglion, small but distinct thickenings of the li\ i)<)(li'rnii.s ( I^g. 

 4, 2iid ant). Moreover, these are to be 

 detected in both cross and longitudinal 

 sections (Fig. 5), and bear to the ganglion 

 of the tritocerebral segment the same rela- 

 tion which we should expect of appendages. 

 To be sure, not every hypodermal thicken- 

 ing is to be interpreted as the rudiment of 

 an appendage. Since, however, the thick- 

 enings under consideration occur not only 

 in one but in several preparations, since 

 they occur in the location we should ex- 

 pect for such appendages and do not occur 

 between the other pairs of appendages, 

 and since, lastly, they bear the expected 

 relation to the ganglia of the second antennal .segment, I see no 

 other interpretation than that they represent vestiges of api:)end- 

 ages such as are still developed in some of the a]itcr)gote 

 insects. 



The mouth-part appendages rapidly increase in size, and early 

 in the eleventh day the length of the ist maxilla: considerably 

 exceeds that of the second maxillae, while a little earlier these 

 appendages were subequal. Measuring from the caudal angle to 

 the apex, we find the length of the mandibles to be about 55 /x, 

 that of the ist maxilL-e 96 /x, while the 2nd maxilkeare but 70 

 There is no trace of lobulation in any of the mouth jxarts. 



The procephalic rudiment has become prominent and, in the 

 latter part of the eleventh day, appears as a button-shaped swell- 

 ing overlying the mouth. In surface views the mouth can be 

 seen through the rudiment, lying slightly caudad of its center. 

 It is this appearance which has led to the incorrect statement 

 that the mouth develops the procephalon. In embr) os of 



