20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



have taken place more gradually, and the balance between species 

 would not have been so suddenly upset. It is not at all likely that 

 tachinids oviposit so heedlessly as above observed, provided they are 

 subjected to thoroughly normal conditions. 



As far as the recognition of stunted and underdeveloped individ- 

 uals of a form is concerned, there is rarely any difficulty provided 

 one is familiar with the characters. The stunted specimens always 

 exhibit practically the same characters, and if there is any exception 

 the true status of a specimen is quite recognizable. 



Characters 



The following outline of the construction and development of the 

 head capsule in CaUiphora, principally drawn from Lowne (Anat. 

 Blowfly, pp. 114-16), forms a fitting introduction to a consideration 

 of characters, inasmuch as those of the head take precedence over all 

 others in the taxonomy of the Muscoidea. 



The Metacephalon comprises the segmented post-oral portion of 

 the head. 



The Paracepi-ialox, which is formed of the two paracephala, or 

 two lateral procephalic lobes of the nymph, comprises the prc-oral 

 portion of the head. 



The paracephala bear the compound eyes and antennae. 



They are united in front and below and form the epistoma and 

 labrum. 



The portion of the facial paracepJialon behind the epistoma shows 

 three distinct parts. These are two bladder-like swellings, the 

 anterior and posterior ccphaloceles, and the antennal ridge between 

 them. The last is developed by a process from each of the two 

 lateral procephalic lobes. 



The anterior and posterior cephaloceles correspond with the thin 

 portion of the blastoderm which intervenes between the two lateral 

 lobes or paracephala. 



The posterior cephalocele is the forehead (Vorderkopf) of the 

 German embryologists. It bears the ocelli, and the front is devel- 

 oped from it. 



The anterior cephalocele develops into the facial region. 



Behind the front there are two plates which extend forward from 

 the metacephalon ; these form the epieepliah)t ( parafro)ital-occipital 

 ridge). 



That portion of the procephalic lobe which lies in front of the 

 antennal ridge unites with its fellow, and curves downward and 

 backward over the mouth to form the prefacial region. 



