AND PHYSIOLOGY OP THE SPONGIAD^. 
809 
established modes of propagation : 1st, by ova ; 2nd, by gemmation ; and 3rd, by spon- 
taneous division of the sarcode. The terms ova and gemmule have been used so indis- 
criminately 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 previous 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 Spongiadae : — 
1st. By ova without an ovarium. 
2nd. By ova generated within ovaria. 
3rd. By gemmules secreted within the sponge. 
4th. By gemmules produced externally. 
6th. 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 confined 
to the true sponges, the genus Spongia. If we examine 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. JoHXSTON 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 
that tribe of sponges, and no other reproductive bodies have, I believe, been discovered 
in the true sponges ; but in arriving at this conclusion we must not fail to remember 
that our knowledge of these animals in the fleshy and solid condition in which they are 
when alive is so limited, and so few observations have been published regarding them in 
that state, that we must not attach too great a value to these conclusions. 
In size and form these ovoid vesicles are very similar to the ova liberated from the 
well-characterized ovaria of other marine species of Spongiadse, and, like them, they 
present no appearance of a nucleus. They are somewhat irregular in their form, and 
vary to a slight extent in size ; an average-sized one measured i^ch in 
diameter. Fig. 6, Plate XXXIII. represents a portion of a fibre from a Bahama sponge 
under a power of 400 linear, and fig. 7 a part of the same fibre xI250 linear. 
Until very recently, our knowledge of the vesicular ovaria of the Spongilladse has 
been confined to two European species; but Caetee, in his excellent account of the 
Spongillas found in the water-tanks of Bombay, has described several new and interest- 
ing varieties of these organs ; and I have also become acquainted with eight new species 
from the Kiver Amazon, through the kindness of Mr. Bate, and of three undescribed 
species from North America, through the kind and liberal assistance of Dr. Asa Geay, 
