224 THE GROUSE IN HEALTH AND IN DISEASE 



transferred to plain water it will live for several days, but show no growth 

 or further development. Evidently there is only a sufficiency of reserve sub- 

 stance within the ovum to develop the embryo to the time of hatchino-. When 

 there is enough food, but the medium is very aqueous, the worm requires to 

 exert itself to a much greater extent in order to entrap small solid 



The first 



moult or particles of food into its rigid and chitinous mouth capsule. If, 

 however, the culture is of such consistency that the embryo is able, 

 by burrowing its way through the faecal matter, to force this into its mouth 

 capsule, there follows a very rapid growth in size and early differentiation of 

 tissue, even when there is a marked lack of oxygen. Under these favourable 

 conditions of food supply an embryo increases in size to such an extent that 

 on the fourth or fifth day from the commencement of the culture it is obliged 

 to shed its cuticular covering. At this time thousands of very delicate 

 sheaths may be found floating in the culture for a few hours ; but they very 

 rapidly disappear. 



The embryo now measures about 0'46 mm. in length, the oesophagus 0'12 

 mm., the anus line 0'08 mm. from the tip of the tail (Fig. 23). 



An excretory pore is to be seen 0'09 mm. from the anterior end of the body, 

 and at 0'24 mm. from the anterior end there is now visible a small clear globule 

 O'OOS mm. in diameter lying on the ventral surface between the body wall and 

 the wall of the chyle intestine. This is the rudiment of the future genital 

 system. A marked difference is now noticeable in the chyle intestine. Three 

 large well - developed valves are seen governing the entrance to it from the 

 oesophagus. Its lumen is widely dilated, O'Ol mm. in diameter, and is filled with 

 ingested fseces. The cells of the gut wall are flattened and very finely granular. 

 No gross structural alterations accompany this first moult or ecdysis, but 

 during the succeeding three or four days certain changes within the body of 

 the worm gradually become evident. 



The cylindrical mouth capsule (Fig. 24) slowly loses its clear cut border and 

 appears to be undergoing absorption, and its lumen decreases (Fig. 25). At 

 Themeta- the same time the oesophagus lengthens, the bulbous posterior portion 

 morphosis. b ecomes pyriform, and later merges into the anterior portion, but so 

 gradually as to be only definable with difficulty. The cuticular lining of 

 the whole oesophagus, and the marked triradiate lining of the cesophageal bulb 

 (Fig. 24) become resolved into a simple thin cuticular covering (Figs. 25, 26). 

 The walls of the intestine, which have gradually increased in size, become more 



