December 21, 1906.] 



SCIENCE. 



813 



discovering the egg of Encyrtus enclosed in 

 the general cavity of the embryo of the Hypo- 

 nomeuta already voluminous and well ad- 

 vanced. The size of the egg is so small that 

 it was not possible to make more than four 

 or five serial sections of its substance. Its 

 contour is ovoid, distinctly limited, and there 

 is no trace of the shell and pedicel observed 

 before laying. There are in the interior five 

 nuclei in the as yet undivided protoplasmic 

 mass, of which four are smaller, rounded, 

 equal in size, and one more voluminous, placed 

 excentrically, of an irregular lobate form, pre- 

 senting a finer and denser reticulum. It may 

 be stated that the four little nuclei are des- 

 tined to engender by successive proliferation 

 all the chain of embryos while the larger 

 nucleus (paranucleus or amniotic nucleus) 

 constitutes the first outline of the amnion. 



At this stage the egg of the Encyrtus is not 

 surrounded by any membrane. One observes 

 only in its neighborhood the presence of cer- 

 tain mesenchymatous cellules belonging to the 

 host. It is a little later, when the number of 

 embryonic nuclei has risen to eight or ten, 

 that an adventitious cyst commences to form 

 by the drawing together of the mesenchyma- 

 tous elements which apply themselves against 

 the egg and form a clothing of even cellules. 

 As to the amniotic cellules derived from the 

 paranucleus, their role is to form the albu- 

 mino-fatty mass which surrounds the embryos 

 and which serves indeed as food for the young 

 larvae. 



At the end of September the little larvae of 

 the Hyponomeuta hatch, but they feed only 

 upon the debris of the eggs and remain until 

 springtime protected by the covering of the 

 egg mass. In opening these larvae under the 

 microscope it is noted with certain ones that 

 there are sometimes two or three little rounded 

 bodies still difficult to distinguish floating 

 among the viscera. These little bodies are 

 the eggs of the Encyrtiis. Examined by 

 transmitted light at the end of autumn, the 

 egg shows a globular or ovoid mass of proto- 

 plasm in which are situated, first, a mass of 

 embryonic nuclei pressed together to the num- 

 ber of from fifteen to twenty; second, a large 



excentric paranucleus frequently divided into 

 two segments. 



This condition just described persists al- 

 most without modification through the winter. 

 Meanwhile in a considerable number of eggs 

 may be found, in the month of March and 

 even in February, a grouping of the embryonic 

 nuclei which already announces the divi- 

 sion of the germ into several embryos. The 

 formative vitellus (characterized by its clear 

 tint) is divided into several rounded masses 

 isolated from each other and each surrounding 

 a group of nuclei. These last, which formerly 

 had two nucleoli, now show multiple nuclei 

 often placed in two rows. 



But the phenomenon of polyembryony 

 reaches its greatest intensity at the period 

 when the young larvae of the Hyponomeuta 

 leave their winter shelter and commence to eat 

 the leaves. 



The egg, at first spherical, grows with an 

 extraordinary rapidity and takes upon itself 

 little by little an elongated ellipsoidal form. 

 It is of this shape and with a considerably 

 increased diameter that it is found in the in- 

 terior of the larvae of H. cognatella about the 

 twentieth of April. The same condition is 

 found in H. mahalehdella toward the tenth of 

 May. 



Studied at this time in a fine cross-section, 

 the germ of Encyrtus is found to be composed 

 of small, rounded masses, which have already 

 in certain instances commenced to shape them- 

 selves at the end of winter. 



Having become more numerous, these are 

 formed of small collections of protoplasm sur- 

 rounding the nuclei (to the number of eight 

 to twelve to each mass) and offering already 

 quite distinct cellular limits. Each one of 

 these masses is lodged in a round and well- 

 differentiated cavity hollowed out of the com- 

 mon nutritive granular protoplasm. These 

 bodies, which may be likened to gemmules and 

 which may be called hereafter muriform, in- 

 crease by the multiplication of their elements 

 until reaching a certain size — each one com- 

 prising then twelve to fifteen cellules — they 

 divide by cleavage. 



In the latter days of April, when the com- 

 plex polygerm of Encyrtus has reached a half 



