go ASCIDIANS CHAP. 



united in little groups which are connected by stolons. The last 

 genus contains one species, Ch. reticulaPus, in some respects a 

 transition-form between the other Polystyelidae and the Styelinae 

 amongst Simple Ascidians. 



Budding in Holosomata — In the Polystyelidae, according to 

 Eitter,! the budding is of the same type as in Botryllidae, the 

 bud arising in each case from the lateral body -wall of the parent. 

 In Botryllus" the oozooid formed from the larva gives rise at 

 a very early period to the first blastozooid of the future colony. 

 This then forms the two buds of the second generation on its 

 sides (see Fig. 55), and these in their turn form the third, and 

 these the fourth generation, in which there are thus eight blasto- 

 zooids ; and so the process goes on, the buds of each generation 



arrangina: themselves in a circle to form 



,® ^'x ^ system. As each new generation 



/A..-- '"frv "■- makes its appearance, the preceding one 



(aX/I .,-- — -,, \\~\5 undergoes degeneration, and is eventu- 



/ ■' A— (STT)— A '; '■ ^^J absorbed. Consequently, in a system 

 '. '. \-.. ^5 --T ■■' r\ ^^^'^^ ^^^ usually be seen, in addition 



©~-i^ Gf/~^ to the adult members, certain older 



~'-., \^ r ,/ ones in various stages of degeneration 



~®- ^ and removal, and certain younger ones 



FiQ. 55.— Diagram to illustrate arising as buds on the sides of their pre- 

 the budding and formation ^ecessors, or lust separated from them, 



of a system m Botryllus. . 



Ooz, oozooid -,311, first and ready to take their places as young 

 blastozooid ; 2 2 etc sue- ascidiozooids in the system. Three dis- 



cessive generations oi buds. •j 



tinct generations are thus commonly 

 seen in a system. Now and again one or two young ascidio- 

 zooids become squeezed by the pressure of their neighbours out 

 of a system into the surrounding test, and so give rise to new 

 systems which add to the extent of the colony. 



Sub-Order 3. Ascidiae Luciae. 



Free-swimming pelagic colonies having the form of a hollow 

 cylinder closed at one end (Fig. 56). The ascidiozooids forming 

 the colony are imbedded in the common test in such a manner 

 that the branchial apertures open on the outer surface and the 



' Journ. Morph. xii. 1896, p. 149. 

 2 See Pizon, Ann. des Sci. Nat. 1" ser. Zool. xiv. 1892. 



