Dr. Holló Ferenc - Dr. Murai Éva szerk.: Parasitologia Hungarica 5. (Budapest, 1972)

can relatively easily be observed through the colourless envelope. The division of the oocyte may begin already in the uterus, hence the deposited eggs occasionally contain zygota or morula of a few cells. The zygota can be found quite near the operculum

,the bicellular morula /25-35 ju/ and the tri- to quadricellular morula /50-60 p,/ in the centre of the egg. The zygota has a round shape /25-32 ja, in diameter/. Of the two cells formed during the first division /inequalis/, the bigger is 26 jju in diam, the smaller 23 yu- in diam /photo 7/. During the subsequent division there is a reduction in cell size /e.g. in the octocellular stage one cell measures 21x21 /x/

, their shape becomes oval then square; at later periods neither cell shape nor cell size can be clearly seen. The development of the embryo is not uniformly rapid even under tne same external /27 C/ and internal conditions /the embryo already exists/. For instance a difference in 1-3 days occurred between the 'hatching of worms from ten selected tricellular eggs. The increase in size of the embryo is demonstrated in Table 3

. Table 3. size of embryo in /u. oviposition 2nd day 4th day 6th day 8th day 10th day hatching 25-35 25-31

x 32-50 40-50* 50-75 45-50

X 55-ll2

y 50-55 70-125 50-55 x 120-130 50-55 X 130-180 50-55 X In the first 5-6 days, no significant change can be observed, except for the growth of the embryo and its oval elongation /photos 810/. On the 6th and 7th days, the terebratiorum appears and the only apical gland, and the four penetrating glands /situated in pairs laterally along the apical gland/ can be followed. On the 6th day, the flame cells, to be found on