192 



PROCEEDINGS OF SOCIETIES. 



Rattles7iake , observed the jelly-like spiculated masses to 

 which he gave the name Thalassicolla. Johannes Miiller 

 subsequently showed that they had been observed by Meyen, 

 and he himself studied them. But it is to his pupil, Pro- 

 fessor Hackel of Jena, that we owe our knowledge of the 

 group. He has published a very large work on them, illus- 

 trated with most beautiful coloured figures (1862). Ehren- 

 berg described the siliceous shells of many of these Radiolaria 

 as Polycystina. A Radiolarian consists of a rounded mass of 

 sarcode, capable of extruding pseudopodia (which Professor 

 Huxley confessed he had missed in his examinations on 

 board ship) ; in this are scattered numerous yellow cells, 

 probably, as Hackel says, acting the part of liver, as we see 

 also in Hydrozoa. In the midst of this is a sac with 

 granules, and a clear nucleus, sometimes containing also 

 curious crystals of sulphate ©f lime. In addition to this, we 

 may have a skeleton, composed either of scattered spiculse, 

 {Sjjhoerozoum) , or a complete enclosing basket-work (Poly- 

 cystina), or radiating siliceous rods {Acanthometra) . These 

 skeletons, which are siliceous, have the most wonderfully 

 beautiful forms, and all this modelling force exists in a mass 

 of homogeneous jelly ! Some Radiolaria are aggregated into 

 masses, as Sphcerozoum, others are single. Their reproduc- 

 tion is but little known. Division has been observed, but no 

 sexual process. In some respects the Radiolaria lead to the 

 Sponges, although perhaps they ought to be regarded rather 

 as a terminal group than as leading anywhere. They are to 

 a small extent rock-makers : as we see in the celebrated 

 Barbadoes earth, which contains Polycystina. 



Spongiad(je . — The structure of Spongilla was described 

 (see Lectures on Classification, p. 14;) as a type. The 

 sponges are to be regarded as aggregations of Amoeboid 

 animals. The ova and spermatozoa are developed in any 

 part of the sponge, and the ciliated embryo, which is pro- 

 duced, encloses the germ or future sponge (fig. 1). It is 



<y4^^ 



tMH^ 



not known if yelk division takes place. The sponges fall 

 into five groups. (1.) HaUsarcida — very simple forms, with 

 no spicula ; the presence of water canals not ascertained. 



