OF THE SPONGIADjE. 133 



believe, both extensive and accurate. I will not attempt a 

 recapitulation of all that has been written on their repro- 

 duction, but content myself with a slight sketch of our 

 knowledge of the various modes of propagation that have 

 been well ascertained and described. From the researches 

 of the various authors who have written on the structure 

 and development of Spongilla and on the marine Spongiadse, 

 it appears that there are three well-established modes of 

 propagation: 1st, by ova ; 2nd, by gemmation; and 3rd, 

 by spontaneous division of the sarcode. The terms ova and 

 gemmule have been used so indiscriminately by authors, 

 that it seems to me advisable to endeavour to define and 

 limit their application in such a manner as to distinctly 

 ' separate the one form of reproductive body from the other. 

 On a careful review of the results of the labours of pre- 

 vious observers and of my own researches, it appears that 

 the following may be considered as the varieties that exist 

 in the modes of the propagation of the Spongiadse : — 



1st. By ova without an ovarium. 



2nd. By ova generated within ovaria. 



3rd. By gemmules secreted within the sponge. 



4th. By gemmules produced externally. 



5th. By spontaneous division of the sarcode. 



On the first mode of propagation by the means of ova 

 generated in the sponge without the presence of ovaria, very 

 little seems to be known, and this mode appears to be con- 

 fined to the true sponges, the genus Spongia. If we ex- 

 amine microscopically the fibres of the sponges of commerce, 

 in the condition in which they come into the hands of the 

 dealers, and before they have been soaked, cleaned, and 

 prepared for sale, we frequently find the fibres covered with 

 innumerable minute -irregularly ovoid vesicular bodies nearly 

 uniform in size, dispersed evenly over the surface of the 

 fibres, and imbedded in a thin stratum of sarcode that coats 

 the membranous sheath that surrounds them. These 

 bodies Dr. Johnston believes to be " the matured gemmules 

 or sporules," and I feel strongly inclined to agree with him 

 in the conclusion that they are the reproductive bodies of 



