BERLESE'S THEORY 53 



The oligopod phase (Fig. 31, C) is derived from the polypod by a 

 process of further differentiation. The thoracic hmbs have 

 markedly increased in size ; the mouth parts have attained fuller 

 growth ; the fundaments of the tracheal system become evident, 

 while the abdominal appendages, excepting those destined to form 

 genitalia and cerci, have undergone resorption. 



Comparison of the embryonic development of various insects 

 shows that the above-mentioned three phases can be identified in 

 varying degrees of definition in different groups. The reader is 

 referred to the standard embryological memoirs, dealing with the 

 more important types, in order to follow the growth changes 

 affecting these phases and the sequence in the ontogeny. The 

 typical protopod phase, for example, is clearly evident in the 

 embryos of Campodea (Uzel), Lepisma (Uzel), (Ecanthus (Wheeler), 

 Xiphidium (Wheeler), Mantis (Viallanes), etc. In these instances 

 the abdomen is at first unsegmented and its metamerism is subse- 

 quently acquired. In other cases the abdomen appears to undergo 

 segmentation simultaneously with the rest of the body, as in 

 Coleoptera. The polypod phase, which immediately follows, is 

 probably an ontogenetic feature common to all Hemimetabola and 

 to many of the Holometabola. In certain of the more specialised 

 members of the latter division all the abdominal appendages 

 may be suppressed from the ontogeny, as occurs in Diptera and, 

 according to Nelson (1915), in the hive bee ; or, the appendages 

 of the first, or first and second segments, alone are developed, as in 

 Donacia (Hirschler), Dytiscus (Th. Bang), and certain other 

 Coleoptera. When the development of embryonic abdominal 

 limbs is thus suppressed it is obvious that a polypod phase, in the 

 strict implication of the term, can scarcely be said to exist. The 

 incidence of the phase can only be inferred from the occurrence of 

 other correlated features such as the presence of spiracles, and 

 the general advance in development following the preceding phase. 

 The oligopod phase is the final embryonic stage among Coleoptera 

 and many Neuroptera ; it probably also occurs in the Diptera and 

 in the higher Hymenoptera, but in a greatly modified and masked 

 condition which renders its recognition by no means obvious. 



According to Berlese the moment of birth, or eclosion from the 



