
454 THE AMERICAN NATURALIST.. [VoL. XXXVI. 
mass, coupled with the passage of individual cells from a resting 
condition, in which mutual pressure gives them a polyhedral 
shape, into an active condition would appear to be the essential 
features of the process and are phenomena not altogether out- 
side our experience. Maas has obviously been led astray in his 
criticism by that well-known condition of mind in which things 
that are not familiar seem impossible. In a more open and 
receptive mood he would probably recognize the fundamental 
differences between the figures of gemmules shown in Pls. XV, 
XVI of my '94 paper and the figures of Fiedler! depicting the 
growth of the ovum in Spongilla, and would not attempt to 
explain the former as variations of the latter; more especially 
when in the same paper (Pls. XXIII, XXIV) I myself repre- 
sent stages in the growth and segmentation of sponge ova (for 
Tedanione and Hircinia), the mode of growth in one species 
(Hircinia acuta) closely resembling that of Spongilla as described 
by Fiedler. 
Since the publication of my results in 1894 there have 
appeared but two communications in which this question is 
touched upon, on a basis of actual observation. Vosmaer and 
Pekelharing? found in Esperella egagropila certain reproduc- 
tive bodies of a problematical nature. Not having at the time 
a sufficiently complete series of stages in the development of 
these bodies, they do “not enter into the question whether 
Wilson's statements about Esperella fibrexilis are applicable to 
our sponge." They confirm my observation that the formation 
of these * gemmules'' is associated with degeneration in the 
structure of the parent sponge, which they find “entirely 
degenerates and finally dies off.” The other communication 
is from Professor Ijima of Tokyo. This author in his recent * 
beautiful and much admired work on the systematic zoólogy 
and histology of the Hexactinellida? reports observations in 
the main similar to mine, and is disposed to draw the same 
,. Ueber Ei und Spermabildung bei Spongilla fluviatilis, Zeitschr. f. swiss 
2 OF tions on Sponges, Verhandelingen der Koninklijke Akademie van 
Wetenschappen te Amsterdam, ı 1898. 
Studies on the Hexactinellida, Contribution 1, Journ. Coll. Sci. Imp. Univ., 
y Pu NE vol. gin Igor. 
