8 



THE SPONGES. 





The 



which approach the shape of the Lithistid phyllotriaene, p. 109. 

 occurrence of pathological branching oxeas is recorded for Petrosia, p. 115. 



Variation. 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 body-shape and general anatomy. 



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

 mens of Hyalonema pateriferwn, p. 24, Canlophacus schalzei, p. 39, Thenea 



fenestrata, p. 84, Petrosia variabilis crassa, p. 114. 



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



In PJurete the spiral 



symmetry, p. 72. 



In Tylodesma alba massive and lamellate bodies occur, 



as parts of one continuous specimen, p. 132. 



In Gellius perforalus a 



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



p. 128. 



In Thenea individuals the number and size of the pore areas 



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



In lophon lamella the character of 



fringe round the osculum, p. 84. 



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. 

 i?. Variation in same individual in the skeletal framework or the skeleton 



in general. 



In Chonclasma calyx the tuberculation of the beams of the dictyonal 

 framework varies, p. 71. 



In Ilexactinella ventilabrum there is considerable 



variation in the way in which the h exacts combine to form the dictyonal 



In Thenea fenestreda there is variation in the develop- 



In Petrosia 



framework, p. 79. 



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



variabilis cr asset, p. 116, and in Petrosia similis densissima, p. 118, a skeletal 



reticulum remains undeveloped in spots. 



In P achy chalina 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- 



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



which project from the surface, p. 128. 



In lophon lamella there is 



















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