CYSTS AND CYSTIPHRAGMS 358 



niiiiutu coiieretioiKs of some iron compound. They react for both ferric 

 and ferrous iron. 



In figure 40 is shown the space actually occupied by an individual 

 polypide. The space occupied by a brown mass and its accompanying 

 cyst or cystiphragms — that is, the space between the distal and proximal 

 diaphragms — is the same as the space occupied by an ordinary polypide. 

 Taking into consideration, therefore, the size, relations to surrounding 

 structures, nature of the material, and its isolation, there can be no doubt 

 that the brown material is due to the replacement, probably by iron sul- 

 phide or iron sulphate, of organic matter left in the zoa'cium after the 

 death of the polypide. 



ALTERNATIVE EXPLANATIONS 



Either this is the case or we must suppose that material injested by 

 the polypide during life has been left in the abandoned zoa'cium. We 

 have failed to see any good evidence that the latter is the case, although 

 there is some analogy for it among the recent Bryozoa. ''I'he appearance 

 of the brown mass and its enveloping cyst is curiously suggestive of the 

 brown body so characteristic of recent Bryozoa. One can not be too 

 careful about being misled by such resemblances; nevertheless there are 

 certain considerations that make it seem to us worth while to suggest the 

 possibility that these cysts and their invariable accompaniment, the brown 

 mass, may actually lia\e been produced in connection with brown bodies. 



First of all, let it be distinctly understood that the brown color of these 

 masses, in the fossil forms, has no relation whatever to the In'OAvn color 

 of tlic oi-igiiial bi-own body; nor is the material, in its present form, in 

 any way simihii-. If there is any relati(ni between the two, we must su])- 

 pose thiit tlie oi'ganie matter of the original bi'own body caused the segre- 

 gation of some iron compound during the decomposition of the former 

 in ihr ahandoncil zon'ciuni. There is plenty of wari'anl among fossils 

 \<tr such a supposition. It might also be possible that material absorbed 

 liy the polypide I'l'om solution oi- suspension in the sea-watei' in which it 

 was li\ing has been excreted and left hehind in the Z0(jecium, after the 

 manner <if the excretion of Bismarck brown and other reagents, as de- 

 seril)ed by Hamier (1.'5). AVe should also have to suppose that after the 

 polypide degenerated into a In-own l)ody the endosarc withdrew or re- 

 treated from the zort>cial wall and formed a new ectosarc enveloping the 

 degenerated polypide. Foi- the deposition of a calcareous cyst about the 

 brown body there is no analogy among the recent l-^ryozoa, so fiir as we 

 are aware; neither is Iheie any analogy for such structures as evsti- 

 pliragms, for that nuitter. It is a fact, however, that intrazou'cial 



