746 PROCEEDINGS OF THE ACADEMY OF [Oct., 



proliferation {Di., fig- 29), which is the perceptible beginning of the 

 diaphragm of the larva. Now also the anterior portion of the ento- 

 dermal canal is nearly cut off from the posterior, it is the immature 

 condition of the larval gland {Gl.) ; sometimes, as in fig. 29, its anterior 

 end is pointed and in contact with the ectoderm of the proboscis, and 

 probably this pointed end represents the beginning of the tube duct 

 of the gland; at least I have no fiurther evidence as to the mode of 

 development of the duct. Fig. 30 shows the ectodermal invagination 

 further progressed, and the gland {Gl.) completely cut off from the 

 intestine {In.)] the mesoderm cells are numerous. In the stage of 

 fig. 31 the embryo is bent upon itself, comma-shaped, since the growth 

 is not of volume but of length, and the double egg-membrane prevents 

 growth in a straight line. The embryo is bent in the region of the 

 diaphragm {Di.). The diaphragm and the whole proboscis anterior 

 to it is ectodermal, except for a few mesenchym cells (shaded) that 

 have now become young muscle cells. Behind the diaphragm, all 

 that region which may be termed the "trunk," we find entoderm com- 

 posing the embryonic intestine {In.) and gland {GL), mesenchym 

 (shaded), and a thin layer of ectoderm which, on the ventral surface 

 near the diaphragm, is thickened (embryonic nervous epitheliiun). 

 Fig. 32 is an immature larva with the armature of the proboscis 

 developed. 



During these stages the ectoderm of the surface of the body becomes 

 very thin, and its component cells fewer in number (compare figs. 27 

 and 31) ; this is evidently due to a participation of the whole ectodermic 

 layer in the proboscidial invagination. In the intestine also the nuclei 

 move to the two ends (compare figs. 29 and 32), so that elsewhere 

 the intestinal wall becomes very thin. The blastopore is completely 

 closed, but its position still marked by the angle of junction of the 

 ectoderm (hypodermis) and entoderm (intestine). The gland loses 

 its central lumen, 



2, The Larva (Plate L). 



The larva is still included within the double egg-membrane, and is 

 not noticeably larger in volume than the egg-cell, so that during all 

 this time it can have taken no nourishment from without. 



A transverse diaphragm (fig. S6, Di.), the margins of which are 

 fused with the hypodermis {Hy.), separates the body into two regions 

 an anterior proboscis and a posterior head-trunk. The diaphragm is 

 with difficulty demonstrable, somewhat thicker than the hypodermis, 

 and staining slightly with ha?matoxyline ; on its anterior surface are 



