162 A Description of the Thread-worm, Filaria immitis. 



end ; except the strongly -marked nucleus the mass was transparent. 

 They were somewhat smaller than those found in the lower end of 

 the uterine canal, and figured at the centre, and to the upper end 

 of Plate XXXI., Fig. 8. Here the average size was -j^ inch in 

 length, by xoW iiich in breadth ; the shape was oval, or approaching 

 that form, the nucleus double or triple, with well-defined nucleolus ; 

 the mass was occasionally divided into two by a transverse line, and 

 granular spermatozoa were detected attached to the germ body as 

 at h, Plate XXXI., Fig. 8, or free among the masses as at e, Fig. 9. 

 It is apparent that at this point in the uterine canal the germ had 

 met with the spermatic fluid, the mass thrown off from the ovarian 

 tubes had become fecundated, assuming an oval outline, and that 

 growth and development had commenced in the multiplication of 

 the nucleus. In the middle third of the uterine canal the ova were 

 in a state of yelk segmentation (Plate XXXI., Fig. 9), mingled with 

 a few free spermatozoa and a few abortive or non-impregnated 

 masses. Higher up the segmented yelk was irregular in shape, 

 with the flexible egg-wall loosely surrounding it ; the form of the 

 embryo was faintly mapped out in some, in others it was clearly 

 defined, while on approaching the double uterine canal, the cavity 

 was observed distended with free embryos coiled up or straightened 

 out (Plate XXXI., Fig. 10, a). Throughout the canal abortive 

 germ masses were to be met with, and the egg-wall, or limiting 

 membrane of the mass, was transparent, flexible, yet easily ruptured 

 by pressure ; some of the ova were as small as xaVo- ii^ch -f- 2 tott iiich ; 

 but as a rule an increase in size took place on impregnation, and on 

 the distinct maturation of the embryo. The ova and embryos were 

 so innumerable that the entire worm was mainly made up of one 

 large germ-containing bag. 



Besides the alimentary and generative system, was the water 

 vascular system. Passing from one extremity of the worm to the 

 other, and clearly shown from the inside by splitting up the musculo- 

 cutaneous parietes, were four main tubes attached to the inner 

 muscular layer (Plate XXX., Fig. 1, e), their walls thick but trans- 

 parent, and freely studded with calcareous corpuscles in common with 

 the " tube charnu " generally, and also the uterine canal. These 

 main tubes were apparently connected with the surface by a series 

 of oval cuticular depressions with circular circumferences, having a 

 central aperture at the bottom of the cup (Plate XXX., Fig. 2, c), 

 communicating with the tube within. Sometimes these breathing 

 orifices were linearly arranged, but generally scattered, and more 

 numerous towards the tail end of the animal. Within the musculo- 

 cutaneous parietes these main tubes appeared also connected with 

 some very delicate ones ramifying between and around the con- 

 tained viscera, and especially numerous towards the ovarian con- 

 volutions ; and in the centre of the body of the worm were on a 



