ORIGINS OF AGAMIC PATTERNS 635 



tentacle development. An interpretation suggesting that parental domi- 

 nance and gradient difference on the two sides of the bud are not entirely 

 obliterated in early bud stages has been offered (Rulon and Child, 1937, 

 p. 10). In some of the corals the apical zooid of the colonial axis is radial; 

 the lateral zooids, originating as buds from its basal region, are dorsiventral 

 and bilateral, with the median plane passing through the long axis of the 

 colony or branch. Each of these lateral zooids, like the lateral branch of a 

 multiaxiate plant, is apparently capable of becoming a radial apical zooid 

 when sufficiently isolated physiologically or physically (Wood- Jones, 

 1912). 



Bryozoan buds represent new longitudinal axes, but their dorsiventral- 

 ity is determined in definite relation to pattern already present in the 

 region of the parent from which they arise. Statoblasts of phylactolaema- 

 tous bryozoa, often regarded as internal buds, develop from the funiculus, 

 a strand extending from the end of the aboral prolongation of the stom- 

 ach, the caecum, to the aboral wall of the zooecium. The funiculus is de- 

 scribed as consisting externally of mesoderm and internally of ectoderm, 

 which enters it from the wall of the zooecium in early stages. The stato- 

 blasts, more or less lentoid in form, develop successively from near the 

 caecal end of the funiculus. An axiate pattern coincident with the short 

 diameter and evidently determined at the time of their formation is pres- 

 ent, and pattern of later development has a definite orientation with re- 

 spect to it. The dorsiventrality of the polypid and localization of the 

 primary budding region are apparently also predetermined in the stato- 

 blast but are not evident until its development. The relation of stato- 

 blast pattern to the pattern of the parent zooid is not entirely clear. In 

 some forms — for example, Cristatella — the short diameter of the stato- 

 blast is said to be coincident with the long axis of the funiculus, and stato- 

 blast formation is a sort of strobilation of the funiculus. In other forms 

 (Plumatella) the short diameter is apparently at right angles to the funicu- 

 lar axis, and the statoblast is perhaps to be regarded as a lateral bud. In 

 either case it seems probable that the statoblast is primarily a bud with 

 a new polar axis, like other buds, but that certain other features of its 

 pattern are determined in relation to parental pattern. 



Various types of budding appear in ascidians: some of the types of 

 development commonly called budding resemble fission rather than bud- 

 ding, and certain others approach development from cell aggregates. The 

 association of certain types of budding in many forms with a depression 

 or degeneration of a parent individual suggests physiological or physical 



