10 W. C. M'Intosli on the Azoic- Mud Theory. 



sides, it is well known that a large quantity of organic matter 

 in solution ("diflfused protoplasm " be it called) exists in many 

 freshwater lochs and ponds ; yet it has not been brought to 

 light that the Rhizopodous faunse of these ever resort to this 

 old prescription of nutritive baths, after the fashion of the 

 Gregarinse and other parasites*. 



Moreover it does not seem to be a sound inference to assert 

 (and this also is a modified form of Dr. Wallich's argument) 

 that, because the Protozoon has the power of " drawing " from 

 the sea-water " the mineral ingredients of the skeleton it 

 forms," it is nourished by direct absorption of the " dilute 

 protoplasm " so conveniently dissolved in the surrounding 

 medium. So far as our experience of such formations goes, 

 the calcareous and siliceous spicula and the horny fibres of 

 sponges, the tests of Foraminifera, and other such organisms 

 are (of course with the exception of the instances in which 

 foreign bodies are used) as much the peculiar secretions and 

 excretions in virtue of the inherent properties of their tissues 

 as the crystalline styles in the gastric organs of certain mol- 

 lusks, the stylets in the Nemertean proboscis, and the spicula 

 of the Echinoderms. It is no rough " drawing " of " mineral 

 ingredients " from the sea-water which takes place at all, but 

 a much more intricate vital process ; for, just as the primitive 

 layers in the vertebrate embryo form the respective classes of 

 tissues, as each annelid produces its characteristic bristles, 

 each Synajota its peculiar anchors and plates, each armed 

 Nemertean its stylets, each mollusk its shell, and each coral- 

 polyp its special mass, so the elementary tissues in the several 

 Rhizopoda as invariably secrete or excrete their peculiar in- 

 ternal or external " skeletons," and that, too, in many cases, 

 as infallibly as though each had inherited the die from its 

 ancestor. It is true that in marine animals the surroimding 

 medium is favourable, but this will not of itself affect the main 

 question at issue. The same line of argument used by the 

 reporters may be applied to every other subkingdom of ani- 

 mals inhabiting the ocean, from mammals to coelenterates ; 

 yet it is highly problematical if a minute coral-polyp would 

 rest satisfied with a meal of this " dilute protoplasm " any 

 more than, in our opinion, a Protozoon would. The specula- 

 tion does not appear to be worthy of confidence. 



3. The Azoic-Mud Theory. 



In the summary of the results of the last cruise of the 



* Tt is a pity the solution of ''protoplasm " was not a little stronger; 

 for thereby many marine animals, such as Arenicoln, would have been 

 saved some trouble. 



