No. 3-] THE EMBRYOLOGY OF A TERMITE. 547 



The origin of the embryonic membranes of insects is referred 

 to the peculiar phenomenon of " doubling-up " exhibited by the 

 myriopod embryonic band. 



It was originally claimed by Will that the invaginations in 

 the two cases are genetically connected to such an extent that 

 some of the posterior segments of the elongated myriopod 

 band, on bending forward, were directly transformed into the 

 amnion in the ancestral insect embryo. In this way the adult 

 insect came to have fewer posterior abdominal segments than 

 the myriopod. 



Judging from Heider's remarks in his monograph on Hydro- 

 philus, no genetic relationship is now meant to be implied 

 between the " doubling-up " of the myriopod embryo, and the 

 invagination to form an amnion in the insects. 



The idea now advanced is, that the resemblance in the two 

 cases is of sufficient importance to intimately connect the 

 phenomenon presented by the elongating myriopod embryo 

 with that observed in Libellulids, which are said to best exhibit 

 what is termed the primitive, invaginate type. The similarity 

 in the two instances, however, is only claimed to be the result 

 of the action of a common cause of the invagination. 



Will's idea of a transformation of a part of the segmented 

 body of the embryo of the myriopod into an amnion for the 

 insect embryo has been abandoned since Graber's (9) criticism. 



Heider in his monograph (13), and in the text-book with 

 Korschelt (17), points out the similarity between the amnion 

 and the rudimentary ectoderm of the embryonic band from 

 which it arises ; and in this is in agreement with what has been 

 observed and figured by most investigators, as I have already 

 noted in another connection. 



D. 2. Recently, Heymons (15) has studied the interesting 

 apterygote Lepisma saccJiarina. As a result, he claims to have 

 furnished us with a convincing intermediate stage between the 

 phenomenon of doubling-up of the myriopod embryo, and the 

 formation of an amnion and amniotic cavity in winged insects ; 

 which he thinks proves that the latter process is directly derived 

 from the former. 



In describing the embryonic rudiment the author speaks 



