4 passages, each of about 3 weeks, were realized with one Locusta С A. and 

 even in the last passage the activity \vas evident. 



3. Injection of C. A. hormone extract. Up till now experiments yielded no 

 results. Mortality was always unduely high, probably the toxic effects of the 

 available extracts override the other effects. 



4. Implantation of ventral glands. 



Morphogenetic effects are not only exerted by the level of C. A. hormone, 

 but also by the activity of the ventral gland. 



This can be demonstrated by extra implantation of active ventral glands 

 (from Vth stage larvae or very young adults) in Und stage larvae. The result 

 is somewhat surprising. The instar in question never shortened as was found 

 by Strich-Halbwachs (1954), but ahvays lengthened. The resulting formal 

 Ilird stage larvae often showed a completely I Vth stage appearance in wing 

 development only. The percentage of larvae omitting the morphologic IVth 

 stage was strongly dependent upon the sex, in males about 70 — 80%, in fe- 

 males about 20%. The larvae omitting a stage ultimately developed into Vth 

 stage adults лvith a normal appearance but smaller and sometimes with лvings 

 resemblingthoseofprothetelicallatectomy Vth stage larvae. This provides some 

 evidence for the theory that morphologic development is governed by a 



Table 1 



Part of experiment showing the effect of implantation of extra ventral glands from Vth stage 



larvae into Und stage larvae (less than 24 hours old) and subsequently reared at 30°C. Means 



are accoinpanied by standard deviations of these means. 



10 Sympos. Evolutio Inscctorum 



145 



