THE VICTORIAN NATURALIST. 71 



If sponges of this species are gathered in the summer, scores of 

 embryos will be found embedded in the gelatinous material 

 supporting the chambers or even in the chambers themselves, and 

 anyone wishing to study the embryology of a sponge cannot do 

 better than commence with Sycon raphanus. For this reason I 

 have figured and described the various stages (see Plate I.) in the 

 development of such a sponge, nearly all of which can be followed 

 without much difficulty. The best methods to employ in such 

 investigation can be obtained from text books which treat of 

 special microscopic technique. 



The next sponge on our list is Sycon gelatinosum, often known 

 under the name given to it by Hasckel, as S. arborea. This is a 

 very common species in Australia and is very variable in form, 

 being either colonial or solitary. The solitary form, about an 

 inch in height, is found attached to the under surface of stones ; 

 whilst the colonial form, which consists of tubes very richly 

 branched, reaches a height of 2 or 3 inches and is found growing 

 amongst the sea-grass on the ocean side of the reef at Flinders. 

 In colour these sponges are a creamy white and in some a fringe 

 of spicules surrounds the oscula whilst in others it is absent. 



A single tube or branch of the colonial form represents a single 

 individual of S. raphanus and if we examine a transverse section 

 of such a tube we notice that the chambers have a radiate 

 arrangement as in S. raphamis but the ends do not project freely 

 as in that form but are enclosed in a cortex which is continuous 

 from chamber to chamber. The presence of this cortex 

 necessitates some change in the canal-system and we find special 

 pore-areas in it through which the water enters. The fores lead 

 into inhalent canals which communicate directly with the 

 prosopyles in the walls of the flagellate chambers through which 

 the water flows; the chambers open by means of very short 

 exhalent canals in the gastral cavity and the stream of water 

 passing out of each chamber is regulated by the opening and 

 closing of a diaphragm with which each chamber is furnished. 



The last example of the group to be considered is one named 

 Vosmaeropsis macera. This sponge is something like S. gelatin- 

 osum in appearance, but the tubes are more densely agglomerated, 

 the numerous individuals being almost completely fused together. 

 We take this form for examination because of the modification of 

 its canal-system as compared with the last example. Here the 

 chambers are thimble-shaped, but they are scattered somewhat 

 irregularly between the dermal cortex and the gastral cavity, and 

 as they lie at some distance from the gastral cavity communica- 

 tion is effected by means of long exhalent canals, whilst in 

 S. gelatinosum these canals are short. 



The calcareous sponges described above do not, of course, 

 exhaust the list of the Flinders specimens. They have been 



