BUDDING IN TUNIC AT A. 49 



case of Botryllus (20). The other organs or tissues of 

 the bud which may be produced directly from the parental 

 organs are — 1. The peribranchial chambers, e.g., primary 

 ascidiozooids of Pyrosoma, Dolioliim (?) ; 2. the peri- 

 cardium, e.g., Pyrosoma, Salpa. (In Dolioliim the peri- 

 cardium of the larva and the pericardial rudiment of the 

 stolon are separated off from the mesoblastic bands at the 

 same time and in juxtaposition.) 3. The genital glands, 

 e.g., Pyrosoma, Salpa, Dolioliim (?), Botryllus. 



The two kinds of budding which have just been 

 described are sufficiently distinct to be entitled to receive 

 appropriate names, and the nature of the distinction would, 

 I think, be adequately indicated by the use of the terms 

 "differentiate" and "undifferentiate" in connection with 

 them. By " differentiate budding " I mean the production 

 of buds by means of a number of special prolongations of 

 the differentiated parental organs ; and by " undifferentiate 

 budding " the production of buds by means of the three un- 

 differentiated germinal layers alone. Botryllus furnishes a 

 connecting link between the two types. In this form the first 

 few generations of buds are produced upon the undifferen- 

 tiate plan, but in later generations the participating meso- 

 derm is differentiated to some extent — the genital cells no 

 longer arise from the mesoderm proper to the bud, but, as 

 Pizon has shown, are transferred in a more or less matured 

 condition from one generation to another. In Clavelina, 

 also, the mesodermal organs of the bud are derived from 

 two distinct sources — the musculature, connective tissue, and 

 blood from the mesenchyme of the parent, the pericardium 

 and heart, on the other hand, from the endodermal 

 (epicardial) prolongation. In spite of the absence of a 

 sharp demarcation between the two modes of budding, I 

 think it desirable to emphasise the contrast between the 

 more typical cases ; and it is a most noteworthy fact that 

 while the "undifferentiate" type is especially characteristic 

 of the fixed Ascidians (Ascidiacea), the " differentiate" type 

 is peculiar to the pelagic forms (Thaliacea). Botryllus, on 

 account of the continuity of its germinal cells through 

 successive generations, furnishes an interesting instance 



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