678 A N^:\v kndoparasitic copepod, 



lined by a flattened epitlieliuiii, and is usually distended with more 

 or less matured ova. The posterior seji;ment or ovidut-t proper is 

 lined by a columnar epithelium (Fig. 29), is of small lumen or its 

 walls are in contact, and does not contain ova. Extending anterior- 

 ly from the .junction of the two segments is a short blind diverti- 

 culum, which may be a receptaculum seminis, but does not contain 

 spermatozoa in any of my specimens (Fig. 1). For a portion of its 

 course, the oviduct proper is freely open to a gland situated dorsal 

 to it (Figs. 1 and ;51), and which probably supplies the material 

 which serves to agglutinate the ova into strings. 



Just within the vulva are two bundles of i)lain nuisde-tibres, 

 which are capable of depressing the floor of the last portion of the 

 duct. Their contraction possibly creates a vacuum which helps 

 in the passage of the ova along the duct(Fig, 32). 



The vas deferens is lined by a columnar epithelium (Fig. 28). 

 Ventral to the digestive canal, thei'e is a tubular connection be- 

 tween the two external male orifices. This tube may be a vesicula 

 seminalis ; it is lined by a syncytial epithelium, and in its walls are 

 a few plain muscle-fibres ( Figs. 27 and 30). 



Development. — The mature ovum is of the typical egg-shape, 

 even to having a thicker and a thinner end ; its subsequent history 

 shows the thicker end to correspond to the posterior pole of the 

 embryo. The nucleus is large; a chromatin network and nucleolus 

 are plainly visible in a perfectly hyaline nucleoplasm. Yolk- 

 spherules are plentiful, and are quite evenly distributed throughout 

 the cytoplasm. 



Cleavage. — The first and second cleavages are parallel to the 

 long axis of the ovum, and at right angles to each other. 



Figure 33 is drawn from a section made at right angles to the 

 long axis, through an embryo in the two-cell stage. The nuclei in 

 this and otlier early cleavage-stages (four- and eight-cell stages) 

 are surrounded by areas of cytoplasm comparatively devoid of 

 yolk-spherules; this area is probably traversed by achromatic 

 astral rays that are too fine to be seen in my preparations. Fig. 10 

 is a drawing of the reconstructed two-celled embryo. 



