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Development of the sense organs of the larva of Botryllus schlosseri
Author(s) -
Grave Caswell,
Riley Gordon
Publication year - 1935
Publication title -
journal of morphology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.652
H-Index - 74
eISSN - 1097-4687
pISSN - 0362-2525
DOI - 10.1002/jmor.1050570111
Subject(s) - biology , ectoderm , anatomy , sense organ , primordium , ganglion , blastema , nervous system , larva , commissure , embryo , embryogenesis , regeneration (biology) , microbiology and biotechnology , neuroscience , botany , biochemistry , gene
A study of the development of the sense organs of the larva of Botryllus schlosseri to determine, if possible, any homologies between its sense organs and those of other types of ascidians such as Molgula and Ammaroucium, which have sense organs structurally very different. The statolith appears in the Botryllus embryo as a single club‐shaped cell. The lightsensitive organs have their primordia slightly later as five small filaments, each developed from a ganglion cell. A cavity appears in the statolith into which the light‐sensitive filaments penetrate. Later development is concerned with pigmentation of the statolith, and a twisting process which orients it into the position in which it is found in the free‐swimming larva. The three tactile papillae develop from evaginations of ectoderm at the anterior end of the embryo. The ectodermal cells at the center of a papilla are differentiated into rod‐shaped sensory receptors and ganglion‐like masses of nerve tissue. Nervous connections are established between these peripheral ganglia and the central nervous system. Results of the investigation indicate that the statoliths of the different ascidian larvae are homologous; the direction eyes probably are not, but have evolved independently from a light‐sensitive area in the primitive larva of a common ancestral ascidian. The larvae of Molgula and Ammaroucium possess no structures comparable to the sensory papillae of Botryllus.