Sperry P J, Ansevin K D
J Embryol Exp Morphol. 1975 Feb;33(1):85-93.
Lateral fragments which contained no nerve cord were isolated from the postpharyngeal body section of Dugesia dorotocephala and fused with nerve cord grafts soon after isolation and at daily intervals through 8 days of regeneration. Fragments fused soon after isolation formed "headless" regenerates but had normal body proportions. If the lateral cordless fragment was allowed to regenerate for 1 day or longer before fusion with the nerve cord fragment, the head always developed and the body proportions were normal. Therefore, head structures become determined in the lateral fragment within the first 24 h of regeneration; during this time these tissues can also respond to the head-inhibiting influence of the nerve cord. The competence to form particular structures of the postcerebral body regions must emerge after head-forming competence is lost, that is about 24 h after isolation; however, it persists at least through the first 8 days of regeneration. Normal body proportions can be induced by nerve cord grafts throughout the first 8 days of regeneration. Lateral fragments fused at any time after isolation with another fragment containing no nerve cord developed head structures but failed to differentiate tissues of the postcerebral regions. This confirms that the nerve cord is responsible for inhibition of head structures and induction of differentiation of body regions and normal body proportions.
从多头涡虫咽后体节分离出不含神经索的外侧片段，并在分离后立即以及在再生的8天内每天与神经索移植物融合。分离后不久融合的片段形成了“无头”再生体，但身体比例正常。如果外侧无神经索片段在与神经索片段融合前允许再生1天或更长时间，头部总是会发育，且身体比例正常。因此，头部结构在再生的最初24小时内在外侧片段中就已确定；在此期间，这些组织也能对神经索的头部抑制作用做出反应。形成脑后身体区域特定结构的能力必须在失去形成头部的能力之后出现，即在分离后约24小时；然而，它至少在再生的前8天持续存在。在再生的前8天内，神经索移植物可诱导正常的身体比例。分离后任何时间与另一个不含神经索的片段融合的外侧片段发育出头部结构，但未能分化出脑后区域的组织。这证实了神经索负责抑制头部结构并诱导身体区域的分化和正常身体比例的形成。
