336 PROCEEDINGS OF SECTION D. 



presence of such stages as shown in figs. 26 and 27, compared with 

 those shown in figs. 19, 20, and 21, is very difficult to understand. 



The larva (figs. 28 and 29) is now definitely outlined, and 

 consists for the most part of two, three, or four layers of cells, 

 regularly arranged, but showing here and there spherical nuclei, 

 staining pinkish with Giemsa, as contrasted with the double row of 

 purplish nuclei, of which the body is chiefly composed. At this 

 stage the head is often differentiated, and rarely and indistinctly the 

 beginnings of the V and tali-spots may be detected, becoming more 

 definite very soon. The normal position of the larva in the latter 

 part of this stage is in a flattened open coil, the head being nearest 

 the enveloping egg membrane when present with the tail to the 

 centre of the coil. Its length is usually 0.155 mm. The whole egg 

 measures at this stage 0.043 to 0.045 mm. by 0.03 to 0.039 mm. 

 In contradistinction to many forms the egg of this worm does not 

 appear to possess an egg-shell invariably, or even usually, in its 

 earlier stages, as shown in figs. 13 to 23, a fact which mainly accounts 

 for the absence of empty egg shells, observed and commented on by 

 Cleland and Johnston. Occasionally, however, a delicate homo- 

 geneous enveloping membrane, but with more deeply staining spots, 

 is to be seen round the immature larva, for example, fig. 24. Evi- 

 dently the adaptation of the egg to its environment does not 

 require the constant presence of any special egg shell. 



The normal dimensions of the newly-liberated larva are 0.23 

 to 0.35 mm. long by 0.0031 to 0.0041 mm. wide ; no sheath is 

 apparent. The larvae when free in the common uterus are some- 

 what wavy and closely packed together. When free, whether in 

 the surrounding fluid or traversing the fibrous capsule, their 

 body is distinctly undulating, the head being straight and the tail 

 sharply recurved. 



The larva is now marked out more or less definitely into five 

 areas. The extreme anterior (0.0025 to 0.0049 mm.) and posterior 

 (0.0093 to 0.0132 mm.) ends are more or less hyaline in appearance, 

 being devoid of nuclei. The distance of these areas from the 

 anterior ends, as seen in a typical larva of 0.25 mm., are, to the V 

 spot, 0.06 mm., thence to w 0.071 mm., thence to x 0.048 mm., 

 thence to the tail spot y 0.031 mm., thence to the tip of the tail 0.04 

 mm., and these figures may be taken as giving the average position 

 of the areas in question. The extreme anterior end appears rarely 

 to carry a spear-like process which stains more deeply than the rest 

 of this hyaline portion. Immediately succeeding this hyaline head- 

 end are two rows of long elliptical nuclei, one of which is often in 

 advance of the remainder. Just in front of the well-marked spot, 

 about 0.05 mm. from the anterior end, is a group of finely granular 

 cells, evidently the rudiment of the nerve ring. The nuclei are 

 much more densely packed just in front of and just behind the V 

 spot ; behind this again they are more separated, until just behind 

 the indefinite gap often present at w they are most closely arranged. 

 The gap at x is also often very ill-defined, the nuclei being, howe\'er, 

 crowded back to and behind the very sharply-marked spot y. 



