BIOLOGY OF PARACOPIDOSOMOPSIS. 365 



laying of the egg and the emergence of the adult insects; whereas 

 in the cooler months of October and November, it takes about 

 40 to 45 days. 



II. THE EARLY POLYGERM STAGE. 



It will be sufficient, for the purposes of this paper, to give only 

 a brief statement concerning the early development of the egg. 

 The freshly deposited egg is a pear-shaped structure, with a large 

 conspicuous nucleus situated toward the anterior or narrower 

 end, and a deeply staining nucleolus lying at the posterior or 

 broad end. Immediately after the egg is deposited, the nucleus 

 undergoes the typical maturation divisions. The first polar 

 body nucleus divides simultaneously with the second maturation 

 division. There is thus produced an egg nucleus and three 

 polar-body nuclei. The former then moves to the broad end 

 of the egg, and whether fertilized or not, produces the cleavage 

 cells. One of the first four blastomeres receives the nucleolus, 

 the presence of which somewhat retards the subsequent divisions 

 of this particular cell. By the time the other three blastomeres 

 have produced about twenty-four cells, the one containing the 

 nucleolar substance has produced but four. Beyond this point 

 its history can not be followed. All of these early blastomeres 

 constitute the embryonic cells. They occupy the posterior two- 

 thirds of the egg. 



In the meantime, the polar-body nuclei fuse to form a single 

 polar nucleus, which continues to divide until the protoplasm of 

 the anterior end of the egg is filled with nuclei. The anterior 

 third of the egg thus becomes syncytial in character, and may 

 be called the polar region. In slightly later stages the polar 

 region completely surrounds the mass of embryonic cells, and in 

 stages still more advanced, it forms a nucleated membrane. 



About seventy hours after oviposition, the nucleated membrane 

 begins to invade the embryonic cells by the formation of tra- 

 beculce, which divide the embryonic cells into several groups, or 

 primary masses (Fig. i). During the formation of these masses, 

 or very shortly thereafter, the young polygerm elongates in the 

 direction of the long axis of the egg (Fig. 2). In addition to the 

 nucleated membrane, each primary embryonic mass develops a 



