I9I4'] N. Annandai,e . Fauna Symhiotica Indica. 153 



branching grooves on the surface of the parenchyma easily seen 

 through the colourless dermal membrane that forms their roof. 



The skeleton is composed of single fibres which ramify feebly 

 or not at all. Its exact structure differs considerably in different 

 parts of the sponge. Towards the periphery (pi. xi, fig. 3) the spi- 

 cule-fibres are short, slender and simple; their course is almost 

 vertical; they are somewhat sparsely scattered and they never 

 branch; their upper extremities form comparatively small 

 brushes that support the dermal membrane, hardly penetrating 

 it. The sponge contains numerous tubes made by polychaete 

 worms and in their intermediate vicinity the fibres, which to 

 some extent radiate out from them take on a somewhat different 

 character, becoming longer, branching dichotomously or even 

 trichotomously at the upper end and adopting a more nearh^ 

 horizontal course. It is, however, in the central parts of the 

 sponge that the fibres are best developed, especially at the sides 

 of the superficial exhalent channels. Here they assume a contor- 

 ted but mainly horizontal course, are greatly elongated and densely 

 crowded together. Their upper extremities, indicated b}'' the 

 fact that the pointed ends of the skeleton-spicules are directed 

 towards them, are arranged in parallel lines of fan-like brushes 

 along the sides of these channels, one row on each side, and thus 

 forms a support for the floor of the channels (pi. xi, fig. 2). 



Towards the periphery of the sponge there is no dermal 

 skeleton except a fairly dense la^-er of sigmata, but in the 

 central parts numerous macroscleres lie scattered, without 

 fasciculation, in the dermal membrane. 



Spicules : Megascleres. — The megascleres are slender, smooth, 

 sharply pointed, straight or nearly straight tylostyles with well- 

 defined, narrowly oval heads. The axial tubule is well developed 

 in them, extending into the head. The average length of the whole 

 spicule is about 0-216 mm. and the average diameter 0'0047 mm., 

 the corresponding measurements of the heads being o"oo8 mm., 

 and 00047 mm. ; but considerable variation in size and propor- 

 tions occurs, the total length varying from o-i8 to 0*26 mm. 

 and the diameter of the shaft from 0*004 to 00054 mm. 



Microsclcres. — There are no toxa. The sigmata, which are 

 most numerous in the dermal membrane but also occur singly 

 in the parenchyma, are not grouped in any definite manner. 

 They are smooth and slender and as a rule somewhat twisted in 

 their long axis ; the average sector of their arc is about 0*04 and the 

 average thickness of their shaft 00027 mm. The anisochelae are 

 found scattered sparingly in the dermal membrane and paren- 

 chyma; they are very minute. Their form, in v/hich they differ 

 from those of Mycale aegagropila (Johnston), is best shown by 

 figures (figs, I, la, pi. x); their average length is about o'oiSg 

 mm.; they are the most uniform in size of the spicules and by far 

 the smallest in numbers as well as size. 



Habitat. — Madras harbour in from 4 to 6 feet of water; on 

 shells of living Mytilus latus^ Lara. 



