18 



fui in llie so-called areolae. The first of these is regarded as corresponding to the 

 pores, through which the spines in a MembraniporeUa are connected with the 

 cavity of the zocecium, and the latter is regarded as the adjoining edges of the 

 spines which have formed the two-layered cover. Contrary to Harmer I must 

 however regard the calcified frontal wall in C oernwusa and U. pavonella as a 

 Cryptocyst. It has in reality its origin helow the primary covering membrane 

 of the frontal wall, but there is soon formed on this a fold or out-i)ushing and 

 the Cryptocyst (PI, XIX, fig. 2 b, cr.) grows inside this one, though it is only 

 towards the end of the development of the zocrcinm that it reaches to the distal 

 part, and thus the frontal wall in all younger zocecia shows two proximally directed 

 arched or angular lines not far from each other and springing from the same ter- 

 minal points (PI. XIX, fig. 2 a), of which the distal indicates the ti]) of the just men- 

 tioned fold and the proximal the growing edge of the Cryptocyst. The same is 

 tlie case in the species of the genus Rhaniphostomella (PI. XIX, fig. 19 a). Finally 

 these supposed pores like the other so-named ])ores in the Bnjozoa are not at all 

 apertures, but are filled by a membrane, which must be regarded as an uncalcified 

 part of the wall. This membrane in Umboniiki as well as in many other cases 

 is provided with several small perforations and we have really to do with super- 

 ficial rosette-jjlates here (see rosette-plates and pores). 



As is well known the first zooeciiim in a colony, the so-called primary zofpcium 

 or »ancestrula' (Jullien), frequently shows characters dilTerent from those found in 

 the later zoa-cia and not seldom such which are found in another division, family 

 or genus. In the Cheilostomata it appears typically in the so-called »'/'((/« "-form 

 (Smitt), the greatest peculiarity of which is the possession of a membranous 

 frontal area, which in most cases is suri'ounded by spines and as this form of 

 ancestrula is found not only in malacostegous and acanthostegous Cheilostomata 

 but also in a number of genera {Schizoporella, Escharella, Escharoides, Microporella, 

 Hippothoa), within the division Ascophora, Smitt' and later writers e. g. Harmer", 

 who have studied the question of the genealogy of the Bryozoa, are no doubt 

 quite right in regarding the Tata as an ancestral form of the Clieiloslonidla and 

 the frequency of this Tata-Uke ancestrula as evidence that not only the Aiiasi-a 

 but also the Ascophora descend from malacostegous forms. 



While the ancestrula in some cases (Retepora Beaniana, ^Lepralia- Pallasuma, 

 ^Lepr." spat hii life 1(1 (?), Sinittia reticulata) has the same structure as the common 

 zocecia, in others it has such a structure that it must be regarded as a refiection 

 of a later ancestral form, and sometimes we can even find in the same or in 



' 103 a, p. 235; 99, p. 306; ' 19, p. 321. 



