SEGMENTATION OF THE HEAD OF DIFLOPODA. 613 



two segments. They have probably not yet made their 

 appearance. 



The antennae and mandibles are slightly raised above the 

 rest of the blastoderm^ and each of these appendages shows a 

 slight depression in its centre. The anterior pair of maxilla? 

 are less rounded and smaller than the second pair, and they 

 also lie rather nearer to the middle line. They are most likely 

 homologous with the maxillulae or superlinguaj described by 

 Hansen (1893) and Folsom (1900) in some of the Thysanura 

 and Orthoptera. They are also the homologues of the first 

 maxillae in Cbilopoda and the first maxilhe in Crustacea. 



I am guided to the making of this homology mainly by 

 Hansen's (1893) observation that the structure of the first 

 maxillte in Machilis agrees with that of the second maxilla 

 in the Eumalacostraca, though I am well aware that serial 

 position is of more importance thau structure in such a case 

 as this. 



Folsom's (1900) account of the development of the maxillula? 

 or superlingua3 in Anurida is somewhat unsatisfactory, for he 

 says that they do not make their appearance until some little 

 time after the maxilla? have become evident. This statement 

 may, however, be due to an error in observation, and the 

 ultimate position of these small appendages is between the 

 mandibles and the first maxillte. 



Another piece of evidence which, though structural, seems to 

 me to count for a good deal is this : — My observations on the de- 

 veloping Archispirostreptus have enabled me togiveample 

 confirmation to Heathcote's (1888) statement as to the meso- 

 dermal origin of the salivary gland in Diplopoda. This gland, 

 then, must be a coelomoduct, and is most probably homologous 

 not only with the salivary gland in P eripatus, but also with 

 maxillary gland (in the second maxilla) in Crustacea. 



Hansen has recently (1903) found maxillulse in Scolo- 

 pendrella, and this gives another reason in favour of tlie 

 above-mentioned homology ; for if the Symphyla be not true 

 Diplopods they are, at any rate, very nearly related to them, 

 as they are also to the Thysanura. 



