84 



THE america:n monthly 



[May, 



two canals into one, or leave between 

 them an extremely thin partition. A 

 section of shell through which one of 

 these annelids has mined a passage 

 shows, under the microscope, none of 

 the concave clippings attributed to it, 

 but on the contrary presents a per- 

 fectly circular outline or unbroken 

 curve, as shown in fig. 28, no marks of 



Fig. 28. 



the jaws being seen with a magnify- 

 ing power of 120 diameters — indeed, 

 the path cut by this worm is so pecu- 

 liar and characteristic that when once 

 examined it could never, by any pos- 

 sibility, be mistaken for that made 

 by any other borer. 



The manner in which the sponge 

 is able to work its way through rocks 

 and shells I will not attempt to ex- 

 plain ; but the form or contour of the 

 aggregated sponge-mass, with its ex- 

 tended pseudopodia, corresponds very 

 accurately with the outline of the 

 spaces excavated as shown in 

 figure 27. From the amoeboid 

 character of its living compo- 

 nents, if we admit its power of exca- 

 vating at all, then, every part of its 

 exterior surface possesses that power, 

 and the excavations occupied by it 

 are exactly such as we should expect 

 to find, the monad bodies of which it 

 is composed fitting the concave de- 

 pressions and its pseudopodia the 

 smaller burrows. 



Desmids and Diatoms. 



BY PROF. H. L. SMITH, HON. F. R. M. S. 



I have been interested in the papers 

 upon " Reproduction of Closterium," 

 by Mr. Holland, and on the " Motions 

 of Diatoms," by my friend Mr. Vorce, 

 published in the March number of 



your Journal, and beg to offer a few 

 remarks, not by way of criticism, but 

 simply stating the conclusions that I 

 have arrived at some time since, from 

 the observations of many years and 

 under varied conditions. The "swarm- 

 spores" spoken of by Mr. Holland, 

 are not a mode of reproduction of 

 the desmids. The true reproduction 

 is by conjugation, and the formation 

 of a sporangium, as with the diatoms. 

 It is quite true that moving spores, 

 as observed by Mr. Holland, have 

 been seen and described in the des- 

 mids by numerous observers, and 

 Mr. Ralfs, in the "British Desmidiese" 

 gives a list of those who, at that 

 time, had witnessed this "swarming," 

 and, as something similar does un- 

 doutedly occur with other algae, the 

 conclusion was a very natural one 

 that in the desmids these Avere true 

 reproductive spores. Mr. Ralfs, ad- 

 mitting the fact of "swarm-spores," 

 says, nevertheless, that in the state of 

 science at that time he could not, if 

 this were a mode of reproduction, 

 explain the necessity for the com- 

 plicated process of conjugation, and 

 the formation of a sporangium. The 

 latter he figures, in the case of C/os- 

 terium acerosum, on the authority 

 of Mr. Jenner, as a cell in which the 

 minute fronds of this desmid have 

 commenced their growth, and Oersted 

 has figured the same for Cosmarium. 

 No one, however, has ever observed 

 in the desmidieae, so far as I am 

 aware, that the so-called " swarm- 

 spores" are in any manner serviceable 

 for the reproduction of the plant, or 

 indeed, are at all like the zoospores 

 e. g. of Schizomeris or CEdogoniutn. 

 Wood, in the remarks upon the des- 

 midieae, in his " Contribution to the 

 History of the Fresh Water Algae of 

 North America," does not even men- 

 tion them, giving the true reproduc- 

 tion solely by conjugation. I have 

 observed these spores imprisoned in 

 the cells of Closteriu?n, and moving 

 freely, and have by me the drawings, 

 made years ago; but what is stranger, 

 I have repeatedly seen the same in- 



