MONOGRAPH OF THE NORTH /MEKICAN PROrTOTRYPID.E. 19 



of (Kwnthm nirev.H and its l*arasit« Teleax." Both authors may be con- 

 sulted to the advantage of the student. 



In lieu of original work of this kind I have deemed it advisable to 

 reproduce here a summary of (Janin's work, by Balfour, together with 

 his ligures, in order to illustrate the remarkable changes the embryo- 

 larva must undergo before assuming the normal larval stage. 



Balfour says: 



Tim very first wtages aro unfortiiiiatt'ly but imperfectly known, and the interpre- 

 tations offered by Gania do not in all eases appear quite satisfactory. In the 

 earliest stage after being laid the »'gg is inclosed ir. a eapsulo produced into a 

 stulii (Fig. 1, A). In the interior of the fgg there soon appears a single spherical 

 body, regarded by Gauiu as a cell (Fig. 1, B). lu the next stage three similar bodies 

 appear in the vitellus, no doubt derived from the first one (Fig. 1,C")- The central one 

 presents somewhat different characters to tlie two others, and, according to Gauin, 

 gives rise to the whole embryo. Tiie two peripheral bodies increase by division, and 

 soon appear as nuclei imbedded in a layer of protoplasm (Fig. 1, D, E, F). The 

 layer so formed serves as a covering for the embryo, regarded l>y Ganin as equivaleut 



Fio. 1. — Eiuliryonic (levi'lopuicnt of |>1atyga8ter: A, ejig; B, primitive rcll; C, atlditinnal cells de- 

 vflopetl from the fu-st; I) and E, further cell iilar development; F, final embryonic etage. (After 

 Gauin.) 



to the amnion ( ? serous membrane) of other insect embryos. In the embryo cell new 

 cells are stated to be formed by a process of endogenous cell formation (Fig. 1, D, 

 E). It appears probable that Gauiu has mistaken nuclei for cells in the earlier stages, 

 and that a blastoderm is formed as iu other insects, and that this becomes divided 

 in a way not explained into a 8uj>erficial layer which gives rise to the serous en- 

 velope and a deeper layer which forms the embryo. However this may be, a differ- 

 entiation into an epiblastic layer of columnar cells and a hypoblastic layer of more 

 rounded cells soon becomes apparent in the body of the embryo. Subsequently to 

 this the embryo grows rapidly, till by a deep transverse constriction on the ventral 

 stirface it becomes divided into an anterior cephalothoracic portion and a posterior 

 caudal porticm (Fig. F). The cephalothorax grows iu breadth, and near its an- 

 terior end an invagination appears, which gives rise to the mouth and oesophagus. 

 On the ventral side of the cephalothorax there is first formed a pair of claw-like 

 appendages on each side of the mouth, then a posterior pair of appendages near the 

 junction of the cephalothorax and abdomen, and lastly a pair of short conical an- 

 tennte in front. 



At the same time the hind end of the abdomen becomes bifid, and gives rise to a 

 fork-like caudal appendage ; and at a slightly later period four grooves make their 



