354 CUMINGS AND GALLOWAY MORPHOLOGY OF TREPOSTOMATA 



secretions are made much more freely and extensively in the Trepostomata 

 than in anv other order of Brvozoa. That the brown bodv itself should 

 become enveloped by a calcareous cyst is therefore rather to be expected. 



In the Bryozoa universally the calcareous deposits of the ectocyst are 

 formed in the ectocyst, and not on it — that is, the whole zooecial wall, 

 whether calcareous or chitinous, is thoroughly permeated by the organic 

 matter of the ectocyst (see Milne-Edwards, 21; Nitsche, 26; Ostroumoff', 

 27; Harmer, 12; Calvet, 5, and Levinsen, 20). Hincks (14) states that 

 the ectocyst is a secretion of the endocyst, and this view has been defi- 

 nitely confirmed by Calvet (5). It is evident, therefore, that after the 

 endocyst has retreated from the zooecial wall it secretes a new ectocyst in 

 its new position. By this process the space occupied by the polypide is 

 restricted, and in the event of the foraiation of a complete cyst, as shown 

 in figures 2, 7, etcetera, it is ver}' severely restricted. It is this very 

 limitation of the space occupied by the polypide that constitutes, in our 

 view, the best argument that we are dealing here with a degenerated 

 individual. 



Gregory has suggested that the cystiphragms are for the purpose of 

 strengthening the zocecial walls (11). The fact that these structures 

 ai-e commonly absent near the surface and at the growing tips of branches, 

 where such a function would be best subserved, is, we think, a sufficient 

 answer to Gregory's view. Ulrich (33), with a good deal of hesitation, 

 has suggested that the cystiphragms might represent ovicells. Their 

 great number (in some species) and irregularities of size and arrange- 

 ment and distribution, as well as their sporadic occurrence in many 

 species, are all against this view of their function. The fact that they 

 are invariably empty, that they never contain any foreign particles, would 

 also indicate that they were never in eoniimiiiication witli the exterior of 

 the colony nor with the body cavity. That their function is tlie re- 

 striction of space within the zooecial tube is, we believe, the natural con- 

 clusion from their appearance and relation to surrounding structures. 



In functional zooecia — for example, in the surface layer of zooecia— 

 cystiphragms are often absent or restricted to the proximal portion of 

 the zooecia, indicating that these structures were probably developed 

 somewhat late in the life of the individual polypide. At the growing 

 ends of branches cystiphragms are seldom developed — that is, they are 

 usually absent from the axial region. It is likely that the budding off 

 of new zooecia goes on very rapidly in this region of the zoarium. Each 

 individual is short lived and never develops the characteristics of ma- 

 turity, much less of old age. When, as occasionally happens, the rate 

 of growtli in this part of the zoarium is checked, the individual zooecia 



