EMBRYONIC MEMBRANES 361 



Both Spencer (1926) and Jackson (1928) have definitely shown 

 that they serve this function, and in Perlitus rutilis Jackson 

 mentions that they absorb fatty material from the host and 

 increase notably in size ; in cases where the parasitic larva happens 

 to die the unconsumed membrane cells increases from an original 

 size of about 60/Lt to a maximuin dimension 

 of 580/x. 



According to Parker (1931), " pseudo- 

 germs " or dissociated fragments of the 

 trophamnion in Macrocentris are liberated 

 into the body-cavity of the host. They 

 grow, and also divide by fusion, into many 

 smaller entities and eventually they are 

 consumed by third and fourth stage larvae. 



In some cases the membrane remains 

 intact for a time after the young larva has 

 emerged from the egg. In the Ichneumon 

 Therion morio, a parasite of the caterpillars 

 of the fall webworm in Canada, Tothill 

 (1922) states that the embryonic membrane 

 completely invests the first stage larva from 

 August until the following June. He terms 

 this phase the feeding embryo, since the 

 young Therion grows, and absorbs the 

 body-fluid of its host, while thus enclosed. 

 Grandori (1911) found that in Apanteles ^%!:^^,'^%Zira^^ 

 glomeratus the whole envelope encloses the invested by its 



larva throughout its life. At first it is a embryonic envelope, 



° whose cells have 



complete closed membrane, but subse- assumed the form of a 



quently lacunae form and it assumes the reticulum. (Adapted 

 ^ , : , . from Grandori.) 



condition of a protoplasmic i-eticulum 



(Fig. 92). When the larva is fully grown the protoplasmic 



prolongations break down, and the cells themselves become free, 



but retain their vitality up to the time the parasite bores its 



way out 6f the host. 



Origin of Mixed Broods of Parasites. The factors governing 



the production of broods of polyembryonic parasites, containing 



