Studies in Tunicate development Part II - Abbreviation of development in the Molguldae
Studies in Tunicate development Part II - Abbreviation of development in the Molguldae
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DOI：
10.1098/rstb.1931.0006
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发表时间：
1931-12-01
影响因子：
--
通讯作者：
Berrill, NJ
中科院分区：
文献类型：
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作者：
Berrill, NJ
16个spp。Molgula和Eugyra的2个变种。十个是胎生的。胎生是由于成年体型的缩小（在这个家庭中），反过来又是由于早熟的性成熟，这是由适应沙子的类型在暴露的岩石上定居造成的。卵的大小增加是胎生的结果。九个物种的发展没有形成尾蝌蚪。两种被认为是无尾的物种被发现可以产生蝌蚪。卵裂在无尾目和有尾目的发育中是相同的。在无尾幼体发育过程中，孵化多为破膜而非消化。在这两种发育类型中，在幼虫胃附近总是可以看到细胞的聚集;在有尾目动物中，这是已知的被吸收的尾巴。尾部发育失败是由于脊索细胞部分没有肿胀，然而，脊索细胞以正常数量存在。脊索部分不能伸展导致胚孔关闭延迟。脊索细胞的吸胀在某种程度上取决于周围介质的酸碱度。在139个spp中，海鞘纲无尾海鞘的发育仅限于9种软体动物。在蛇鳗科中，无尾动物的起源是多系的。耳石（唯一的感觉器官）存在于所有的有尾目动物中。幼虫，在所有无尾幼虫中缺席。无尾两栖动物的发育与体型大、卵生和自由的、独立的沙地生活有关;有尾目动物更多地与小的、胎生的、附着的形式有关。第一种类型被认为是原始的，并已二次殖民的岩石。它的结论是，anural发展是一个直接的反应，砂嵌入式的栖息地，孵化酶丢失时，尾巴的发展受到干扰，和anural发展是兼容的种族生存只有当有一个有效的替代方法孵化。
The development of 16 spp. of Molgula and 2 of Eugyra is described. Ten are viviparous. Viviparity is due to reduction in adult size (in this family), in turn due to precocious sexual maturity resulting from the colonization of exposed rocks by sand-adapted types. Increase in egg-size is a result of viviparity. Nine species develop without forming tailed tadpoles. Two species said to be anural were found to produce tadpoles. Cleavage is identical in anural and urodele development. Hatching in anural development is always by inembrane rupture and never by digestion. An aggregation of cells is always seen near the larval stomach in both types of development; in the urodele it is known to be the absorbed tail. Failure of tail development is due to the absence of swelling on the part of the notochord cells, which, however, are present in normal number. Failure to extend on the part of the notochord results in a delay in closure of the blastopore. Imbibition by notochord eells is to some extent dependent upon the alkalinity or acidity of the surrounding medium. Out of 139 spp. of the Ascidiacea anural development is confined to 9 molgulids. Within the Molgulidae the origin of anural development is poly-phyletic. The otolith (the only sense organ) is present in all urodele. larvae, absent in all anural larvae. Anural development is to be correlated with large size, oviparity, and a free, unattached sand life; urodele more with small, viviparous, attached forms. The first type is considered to be primitive, and to have secondarily colonized the rocks. It is concluded that anural development is a direct response to the sand-embedded habitat, that the hatching enzyme is lost when tail development is disturbed, and that anural development is compatible with race-survival only when there is an efficient alternative method of hatching.