[Anatrepsis movements of the germ band in the egg ofAcheta domesticus (Orthopteroidea, Gryllidae)].

1. The anatrepsis movements of the cricket germ band were analyzedi by timelapse micrography and by mechanical manipulation of the egg system. The behavour of isolated groups of germ band cells was recorded in vivo and in vitro. 2. The first phase of anatrepsis is characterized by 7-9 slow peristaltic waves passing within the yolk system towards the posterior egg pole (velocity 26-42 μm/min). 3. During this phase, the germ band moves backwards on the yolk surface. Its posterior end passes the posterior egg pole and then moves on anteriorly along the dorsal midline of the egg. The movement of the germ band is slowed down or reverts its direction temporarily whenever a peristaltic wave of the yolk system approaches the posterior egg pole. 4. In the second phase of anatrepsis, the posterior end of the germ band steadily (1.2 μm/ min) moves along the dorsal midline towards the anterior egg pole, thereby pushing its way in between yolk system and serosa. The remainder of the germ band does not follow suit along the yolk surface of the posterior egg pole but rather takes a short cut through the yolk system which meantime has been divided into yolk cells. 5. If the germ band is cut transversely during anatrepsis, only the part embodying the posterior end of germ band is able to continue movement. 6. Cells from the posterior end of the germ band display pulsating movements when isolated in vitro or in vivo. Cells from other germ band regions do not display such movements. 7. The results indicate that in the cricket egg anatrepsis of the germ band is not, as demonstrated in some other insects, due to pulling forces exerted by the yolk system, but rather appears to be caused by active locomotion of the posterior end of the germ band. Cells located there probably "crawl" along the serosa and pull the germ band trailing behind. The peristaltic waves in the yolk system are thought to ensure close contact between serosa and germ band when the latter passes the curvature of the posterior pole region. Yolk peristalsis is also likely to facilitate movement of the passively transported parts of the germ band.