162 
Psyche 
[June 
(terms of Parsons 1972b). In the metathoracic spiracles of Belo- 
stoma and Ranatra, which also have these two components, the 
integumental region bears the ecdysial opening and is lined by 
epidermis, while the sieve-plate lacks an underlying cellular layer 
(Parsons 1972b). 
The sieve-plate (Figs. 25-27, SV) is composed of branching and 
anastomosing trabeculae (Figs. 28 and 29) which are connected, 
by short struts, to an internal membrane. The fine structure of 
Figs. 25-27. Mesothoracic scolopophorous organs (SO II) and metathoracic 
spiracles (S III), oriented as in Figs. 15-17. Fig. 25. D. zealandiae ; scale line= 100 jum. 
Fig. 26. M. sedula; scale line = 50 pm. Fig. 27. H. interrupta; scale line =150 pm. 
