310 POLYEMBEYONY AND THE DETERMINATION OF SEX. 



with a layer of epitheloid cells and incloses an albumino-fatty mass 

 in which the embryos are immersed. 



Later, after the larva? have attained a certain size (at the end of 

 ■ May or beginning of Jmie), the row, which may have a length of 

 3.5 cm., presents a series of wrinkles and constrictions; each fold 

 contains a larva inclosed in the nutritive substance. At the end of 

 June, after the parasites have completed their first molt, they burst 

 the epithelial tube which enveloped them and are found at liberty 

 within the body of the caterpillar. This period (second larval 

 phase) lasts about eight days. At last, the larvje having consumed 

 the interior of the larva, each one of them prepares for the pupal 

 jjeriod Ijy inclosing itself in an ovoid cocoon, formed, according 

 to Marchal, by the external cuticle puffed out and detached from 

 the body. The caterpillar, the skin of which molds itself exactly 

 over the cocoons, thereafter was little more than a rigid sheath, 

 embossed, and appearing partitioned within. The transformation 

 of the larva into a nymph by means of a new molt takes place a 

 little after the partitioning of the caterpillar, and from the time of 

 this event until the eclosion of the Encyrtus one counts twenty days. 



The Hyponomeutas do not have more than one generation annually. 

 The eclosion of the moth (//. cognatella) takes place in July, copula- 

 tion in the following days; the eggs are deposited a short time after- 

 wards in little clusters of 40 to 70, which the insect attaches to the 

 branches of the spindle tree. 



The young caterpillars, hatched in September or October, rest 

 during six months, crouching under the scaly covering which protects 

 the Qgg mass until the first days of April, before leaving their shelter." 



The facts brought to light by Marchal may be summed up as 

 follows : 



1. Encyrtus is, the same as its host, Hyponomeuta, of only one 

 generation annually. 



2. The oviposition of Encyrtus takes place shortly after that of 

 Hyponomeuta, in Julv or in August, following the species parasitized, 

 and it is into the egg of the moth that the parasite introduces, its 

 own egg. 



3. Each chain of embryos proceeds from a single egg, as a result 



a It is ordinarily between tbe 5th and the 18th of April, exactly at the time 

 when the young leaves of the spindle tree expand, that the minute caterpillars 

 of M. cognatella leave their retreat and I'each the nearest buds. Afterwards 

 hiding in the interior and drawing toward them the leaves by means of a few 

 threads, they form a little nest, which gives them at the same time food and 

 shelter. Their length at this period is from 0.7 to 0.8 millimeter. After this 

 they grow rapidly, but it is only at the end of a few weelvs, after their size 

 has reached about a centimeter, that their webs, having become more volumi- 

 nous, begin to attract attention. {Buynion, 1893, p. 319.) 



