Nos. 455-456-] 



HEAD OF BLATTA. 



Vent. cerv. scl. (gula) 



In each section of the middle column the dotted line indicates 

 the division between the sternal and the lateral elements of the 

 segment. 



My results have convinced me that so intimate a relation 

 between primary segmentation and the sclerites cannot be 

 shown. 



I find that the front, clypeus, and the labrum are all derived 

 from the procephalon. This is in agreement with the conclusion 

 of Zaddach, '54, whose "hinterer Kopf schild " is clearly the 

 clypeits posterior of Newport or the front as defined by Comstock 

 and Kochi. 



Aside from Zaddach practically all authors agree in stating 

 that from the procephalon arise the clypeus and the labrum. 

 It has been suggested by Comstock and Kochi that the term 

 clypem has thus been used in a broad sense to include both the 

 clypeus anterior and the clypeus posterior or the front. 



That H eider used the word clypeus in a yet looser sense is 

 evident. He speaks of the procephalon as giving rise to the 

 clypeus and the labrum. Now, in Hydrophilus, the form upon 

 which he worked, as well as in any of the Hydrophili, the larva 

 does not possess a labrum (Schiodte, '61), or, more correctly 

 speaking, the clypeus and labrum have fused without leaving any 

 line of demarcation between them. Thus Heider has homolo- 

 gized the clypeo-labral sclerite as labrum only, while the front 

 he has mistaken for the entire clypeus. 



On the other hand, Heymons, as is shown by his figures, has 



correctly distinguished the front. 



Yet he states that the clyp- 



and labrum arise from the procephalon, while the front 

 formed from the fused cephalic lobes. He presents no ev 



