46 



BRYOZOA ECTOPROCTA. 



The youngest buds lie, as a rule, at the apex of the branch. In encrusting' 

 colonies, the edge of the colony thus represents the budding zone, from which 

 the further growth of the colony proceeds. In the same way, in Cristatella , 

 the youngest individuals, those in the act of forming, are at the edge of the 

 colony (Fig. 22 kz), while the oldest [dp) lie at its centre. 



BiiAEM has pointed out an important distinction between the relations of the 

 bud to the jiarent in the Phylactolaemata ami in the Gymnolaemata. The 

 colony in the Phylactolaemata arises in such a way that the oral side of each 

 individual is directed towards the distal end of the branch to which it belongs. 

 The younger individuals thei'efore bud out on the oral side of the older (Fig. 22). 

 In the Gymnolaemata, on the contrary, the individuals are placed in the 

 opposite way, each new bud arising on the anal side of the parent {ef. Fig. 24). 

 A similar distinction between the two groups is found in the position of the 

 separate individuals witli resjiect to the substratum. In the Phylactolaemata 

 the individuals, in a withdrawn condition, turn the oral side to the substratum, 

 while in the Gymnolaemata the anal side is thus turned. The attempts made 



by BiiAEM and Davexpout to 

 trace back these different relative 

 positions of the bud and the 

 mother in the Gymnolaemata 

 and the Phylactolaemata to a 

 common type do not seem to 

 us altogether successful. 



BiiAEM presupposes, in the 

 Gymnolaemata, a degenerate 

 primary individual which cor- 

 responds to the distal end (apex) 

 of the stem. Through this 

 assumption he makes the prin- 

 cipal buds of the Gymnolaemata agree with the intermediate buds of the 

 Phylactolaemata. According to Davenport, on the otlier hand, in both 

 groups, each bud turns its anal side to the budding zone from which it has 

 originated. In the Gymnolaemata, this zone lies at the apex of the stem, i.e., 

 distally, but in the Phylactolaemata it lies proximally. To us it appears that 

 in this very point of the position of the budding zone there is no essential 

 distinction between the Gymnolaemata and the Phylactolaemata, since, in both 

 cases, the youngest buds appear distally, that is, at the edge of the colony. 

 Consequently the budding zone must, in both cases, have the same position. 



It has already been pointed out by Nitsche {^o. 52) that two 

 distinct types of budding occur in the Ectoprocta, the Gymnolaemata 

 being in this way opposed to the Phylactolaemata. In the first of 

 these groups the type of budding in which the zooecium forms first 

 is common. In this case the zooecium of the bud arises first as an 

 outgrowth or diverticulum of the parent-zooecium (Fig. 24), and 

 only after this has attained a certain size and independence does the 

 first rudiment of the polypide (^j) appear in it as a bilaminar 

 invagination of the zooecial wall. In the Phylactolaemata, on the 

 contrary, the polypide of the bud appears first, in close proximity to 



Jix 



Fio. 22. — Transverse section through a colony of 

 Cristatella (after Bra em), dp, eldest polypide of the 

 colony, in the act of degenerating ; kz, budding 

 zone. 



