134 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



same character as that already used for the " first maxillte." The labial 

 fiiudameuts are appendages of the seventh somite in botii Hexapods and 

 Crustacea and are supplied by equivalent ganglia and nerves. In both 

 groups each fundau^ent is at first simple and secondarily develops a 

 palpus, or exopodite. Moreover, the axis of the appendage is three- 

 segmented, the segments in Crustacea corresponding to gula, mentum, 

 and palpifers of generalized Hexapoda, the submentum being a secondary 

 development. 



Hansen ('93, p. 206) difters slightly : " Das Submentum [Macliilis] 

 ist mit dem, bei den Gammarinen zusammengeschmolzenen ersten Gliede 

 homolog, das Mentum mit dem bei den Hyperinen auch zusammenge- 

 schmolzenen zweiten Gliede ; auf der Spitze des Mentums findet man eiu 

 Glied, das auf jeder Seite in vier Laden ausgeht, die, wie sich ziemlich 

 deutlich zeigt, zwei Ladeii angehoren, die jede fur sich gespalten ist, und 

 diese halte ich (unter Anderem wegen eines Yergleiches mit Orthoptera 

 und Amphipoda, kann aber keinen zwingenden Beweis von den Skelet- 

 theilen fiihren) respectiv fiir eine Lade vom zweiten Gliede (die innerste 

 gespaltene Lade) und fur das dritte Glied des Labiums mit seiner ge- 

 spaltetem Lade ; der Palpus geht von der Aussenseite des dritten Gliedes 

 aus." 



Hansen should have taken into consideration the gula^ and the fact 

 that the submentum is probably not a primitive sclerite. 



The homologies between Hexapoda and Crustacea that I have defended 

 are none the less valid if the total number of somites differs in the two 

 classes, and they ai'e sustained if the number is the same. In decapod 

 Crustacea there are twenty-one somites, including the ocular segment. 

 In generalized insects the number of abdominal segments varies. In the 

 embryo of Lepisma, which shows marked affinities with Crustacea and 

 Orthoptera, Heymons ('97'') finds eleven abdominal somites. Add to 

 these the thoracic segments and the seven which I have found in the 

 Apterygote head ; and the total, twenty-one, is the same as for decapod 

 Crustacea. In embryos of many families of Orthoptera and Odonata 

 just eleven abdominal segments are present. On the other hand, 

 Heymons ('95*^) has found twelve in certain genera of the same orders, 

 and in Collembola the number varies greatly. In view of this variability 

 within the limits of the same order, then, it is well not to emphasize the 

 agreement between generalized insects and decapod Crustacea in the total 

 number of somites. 



My conclusion regarding the labium, then, is tliat its development in 

 Apterygota conforms to the Orthopteran type. In Anurida a labial pal- 



