112 Annals Entomological Society of America [Vol. XI, 



According to Haase, the eleventh is not an autonomous 

 somite, and Verhoeff a-grees with him. Dewitz states that the 

 eleventh somite is formed only by the doubling of the tenth, 

 and he says that in Decticus this only occurs after hatching. 

 Wheeler shows and labels eleven segments in all the figures in 

 his well known embryological investigations. 



3. Posterior Somites. — The first traces of segmentation 

 are found very early in the germ-band of the insect, which 

 becomes divided by transverse grooves into somites. This 

 process, Heider maintains, even precedes gastrulation in 

 Hydrophilus. This is not a primitive condition however. In 

 the completely segmented germ-band, Korschelt and Heider 

 state, there are ten abdominal somites in addition to the telson, 

 and they give the following observations on the germ-bands of 

 various forms, in proof of this statement : Heider, on the germ- 

 band of Hydrophilus; Graber, on Lina, Stenobothrus, various 

 Lepidoptera and Hylotoma; Wheeler, on Doryphora and 

 Blatta; Cholodkovsky, on Blatta; and Carriere on Chalicodoma. 



In looking over the plates belonging to all the articles 

 referred to by Korschelt and Heider, in each of the above cases, 

 one sees that in the large number of germ-bands figured the 

 terminal abdominal somite is always numbered eleven, and that 

 in no case is the term telson used, that being the name given by 

 Heymons to the twelfth abdominal somite. Of course, mor- 

 phologically, what these somites are labeled may seem imma- 

 terial, and fundamentally it is. However, there is no doubt 

 that considerable confusion has arisen from Korschelt and 

 Heider's statement in this regard. Many invariably take it 

 that, according to these authors, the insect abdomen is typ- 

 ically composed of ten somites and no more. Others may 

 understand that the telson mentioned is formed of the eleventh 

 and twelfth somites fused. As one can see from the work of the 

 investigators themselves, they agree in giving eleven as the 

 typical number of abdominal somites in the germ-bands of the 

 insects upon which they worked. 



One of the difficulties in arriving at any conclusion from the 

 foregoing is that so few investigators have traced structures 

 from embryonic through larval to adult stages, and this same 

 difficulty confronts us when we review the work done on the 

 genital appendages. 



