O THE SPONGES. 



wliich approacli the shape of the Lithistid phyllotriaene, p. 109. The 



occurrence of pathological branching oxeas i.s recorded for Peirosia, p. 115. 

 Vanaiion. The variability of sponges in regard to points of adult 

 structure is universally recognized. 0. Schmidt and Vosmaer, in particular, 

 have laid stress on the phenomenon as bearing upon the problems of 

 systematic classification. The observations recorded in this report will fall 

 under the following heads : — 



1. Variation in hoclz/sTiape and general anatomy. 



Attention may be called to the difference in shape exhibited by speci- 

 mens of Hyaloncma pateriferum, p. 24, Caulophacus schulzci, p. 39, Thenea 



fenestrata, p. 84, Pdrosia variabilis crassa, p. 114. In Eurete the spiral 



form of body beset with cup-like outgrowths varies toward a bilateral 



symmetry, p. 72. In Tt/lodesina alba massive and lamellate bodies occur, 



as parts of one continuous specimen, p. 132. In Gellius pcrforatus a 



uniform habit of growth may result in very different body shapes, 



p. 128. In Thciica individuals the number and size of the pore areas 



vary, pp. 84-85 (comp. especially Vosmaer, 1882, 1885); also the spicular 



fringe round the osculum, p. 84. In lophon lamella the character of 



the surface varies in different parts of the same individual, owing to the 

 divergence in character of the main efferent canals and their apertures, and 

 to the varying amount of collenchyma round such canals, pp. 142-144. 



2. Variation in same individual in the skeletal framework or the skeleton 

 in general. 



In Ghonelasma cidi/x the tuberculation of the beams of the dictyonal 



framework vai-ies, p. 71. In Hexactinella ventilabrimi there is considerable 



variatiuu in the way in which the hexacts combine to form the dictyonal 

 framework, p. 79. In Thenea fenestraia there is variation in the develop- 

 ment of the spicular fringes round the pore areas, p. 85. In Petrosia 



variabilis crassa, p. 116, and in Petrosia siyyiilis densissima, p. 118, a skeletal 



reticulum remains undeveloped in spots. In PaeJujchcdina acapidcensis 



the skeletal framework in places is fairly regular, although in general irreg- 

 ular, p. 122. In Phakellia lamelligera the skeletal lamellae vary in respect 



to branching, p. 153. In Petrosia similis densissima over some parts of 



the surface there are no projecting spicules, while over other parts such 



spicules are present in considerable number, p. 118. In Gellius per- 



foratiis there is considerable variation in the character of the spicular tufts 

 which pi'oject from the surface, p. 128. In lophon lamelbi there is 



