ANATOMY, HISTOLOGY, AND GENERAL. 
Spong. 7 
IL— -MORPHOLOGY, EMBRYOLOGY, PHYSIOLOGY, 
and GENERAL. 
a. Anatomy, Histology, and General. 
Bidder (3), in a short note, confirms Vosmaer and Pekelharing’s obser- 
vations ns to the non-existence of Sollas’s membrane, and promises a 
detailed account of the collar-cells in Sycon compression. 
Ciiopin (7) gives a brief account of the history, structure, develop- 
ment, classification, and distribution of Sponges. 
Dendy (13) continues his Studies on the Comparative Anatomy of 
Sponges,” and gives an account of the structure and classification of the 
Calcarea Heteroccela. According to this author, the canal system varies 
greatly, even in genera apparently closely allied. The Leuconoid type 
has beeu independently developed from the Syconoid type no less 
than three times, but never directly from the Homoccele type. We 
find the Leuconoid type amongst the Orantidce ( Lelapia , Leucyssa, 
and most species of Leucandra ), amongst the ffeteropidcc (Vosmaer apsis, 
which genus is indeed not typically Leuconoid, but rather Sylleibid), 
and amongst the Amplioriscidce (several species of Leucilla ). Five 
stages can be distinguished in the evolution of the most complex Leuco- 
noid from the most simple Syconoid form : — (1) Sycetta stage : the 
flagellated chambers are straight, unbranched, radially arranged, not 
touching each other, without dermal cortex. (2) Sycon stage : the walls 
of the adjacent chambers fuse, leaving between them the “ intercanals.” 
(3) Grantia stage : the distal ends of the chambers and intercanals are 
covered over by a dermal cortex, containing true inhalent pores. (4) 
Sylleibid stage : the chambers are no longer arranged radially around the 
central gastral cavity, but around the usually radial exhalant canals. 
(5) Leucandra stage : the chambers are small, spherical, irregularly 
scattered. 
The starting-point for the development of the skeleton is the radially 
symmetrical skeleton of Sycetta , which is characteristic of the group, 
and obviously dependeut upon the primitive radial symmetry of the 
canal system. The first great change in the skeleton is brought about 
by the development of a dermal cortex, with its special skeleton. The 
skeleton of the chamber layer of the sponge-wall now begins to vary. 
This variation may either depend upon the gradual change of the canal 
system from the Syconoid to the Leuconoid condition, whereby all 
radial symmetry is lost, or may be independent of the canal system, 
such a variation being of the utmost systematic importance. These 
modifications consist in the development of subdermal sagittal 
triradiates ( Heteropidce ), or subdermal quadriradiates ( Amplioriscidce ). 
These newly-developed spicules, with their inwardly directed apical rays, 
replace thus to a certain extent, by a kind of secondary centripetal radial 
symmetry, the primitive symmetry which had been lost in these families. 
