GENERAL DISCUSSION. 

 Chalon's analyses of algse. 



55 



These recent analyses, from the memoir of Madame Lemoine, agree well with ours and, 

 notwithstanding Ilogbom's divergent data, strengthen the suggestion that the proportion of 

 magnesia in the alg;e is inlluenced by temperature. 



The material studied by us was carefully chosen by Dr. Howe, with direct reference to the 



purpose of our investigation. Every species was thorouglily identified, its locality was definitely 



stated, and the specimens were remarkably clean antl free from misleading impurities. The 



results obtained by us are therefore as nearly trustworthy as it is practicable for us to make 



them. The significance of the algae in reference to dolomite was already well established by 



previous workers, but our new data strengthen the conclusions which our predecessors had 



drawn.^^ 



GENERAL DISCUSSION. 



In the foregoing pages we have reported 322 new analyses ol marine invertebrates and have 

 cited many other analyses made elsewhere. These data shed much light upon the chemistry 

 of the marine sediments, anil they also suggest various problems, some of them biological, 

 which are yet to be solved. The limitations of our research have been pointed out in the intro- 

 duction to this memoir and are taken for granted in the following general discussion of the 

 results that we have obtained. First in order we may consider the distribution of the essential 

 constituents of the invertebrate skeletons, taking each one separately. 



Silica. — The skeletons of radiolarians and diatoms and the spicules of siliceous sponges 

 consist almost entirely of opaline silica. The radiolarian and diatom oozes of the Challenger 

 expedition show the importance of tliese organisms. In our own work we have stuched only 

 the sponges, and our results show nothing new. Our analysis of Euplectella, however, is 

 probably more complete than any previous analysis of a siliceous sponge. We have found 

 recorded in the literature only partial analyses of sponge spicules. 



In nearly all our analyses, in every group of organisms, silica appears, generally in small 

 but exceptionally in rather large proportions. Some of this may be essential, but in most cases 

 it is an impurity. In fact, sand grains were distinctly visible in some of the specimens analyzed, 

 but were not readily removable. 



Alumina and iron, oxide. — In most of our analyses alumina and iron oxide were usually 

 determined, but they are to be regarded generally as impurities due to adherent silt or mud. 

 Iron is doubtless a normal constituent in small amounts. 



Lime. — The most important base in nearly all marine shells or skeletons, whether verte- 

 brate or invertebrate, is lime. Only the siliceous organisms arc free from it. MoUuscan 

 shells, the stony corals, the hard parts of millepores, some brachiopods, and the barnacles are 

 composed almost entirely of calcium carboiuxtc and contain only minor impurities. In the 

 other series of marine invertebrates, with few exceptions, it is the dominant inorganic con- 

 stituent. Calcium phosphate and sulphate were also determined in most of our analyses, but 

 they will be considered in other paragraphs. 



Magnesia. — One of the most interesting results of our investigation is the discovery that 

 magnesium carbonate is much more widely distributed as an essential constituent of marine 

 invertebrates than it has hitherto been supposed to be. In the Foraminifera, alcyonarians, 

 echinoderms, crustaceans, and coralline algie it is especially important, and some other organ- 

 isms contain it in notable proportions. Its peculiar relations to temperature have been noted 

 in several sections of this work and will be discussed more fully later. 



" On the importance of alga; as reel builders, see an interesting paper by Dr. Howe in Science, new ser., vol. 35, p. 837, 1912. He cites much 

 other literature. 



