450 



COMPOSITE RIIIZOPODA I — THALASSICOLLIDA. 



type. Each of these bodies appears to be without any direct con- 

 nection with the rest ; but it serves as a centre around which a 

 number of minute yellowish -green vesicles are disposed. Each of 

 these groups is protected by a Siliceous skeleton, which sometimes 



Fig. 237. 



'fC/ r 



SpTusrozoum ovodimare, one of the Thalassicollida. 



consists of separate spicules (as in Fig. 237), but which may be a 

 thin perforated sphere like that of certain Pohjcystina (§ 402), 

 sometimes extending itself into radiating prolongations. The 

 internal portion of each mass is composed of an aggregation of 

 large vesicle-like bodies, imbedded in a softer sarcodic substance. 

 Notwithstanding the subsequent observations of Miiller and 

 Haeckel, * much obscurity still hangs over the real nature of these 

 bodies ; and as they so abound in the seas of warm latitudes as to 

 be among the commonest products of the tow-net, the Microscopist 

 who has the requisite opportunity should not neglect the careful 

 search-for and observation of them. 



* See Huxley in "Annals of Natural History," 2nd Ser., Vol. viii. 

 v 1851), p. 433 ; and " Quart. Journ. of Microsc. Science," Vol. iv. (1856), 

 p. 72 ; also Miiller in his Treatise " Ueber die Thalassicollen, Polycystinen, 

 und Acanthometren des Mittelmeeres," originally published in the 

 Transactions of the Berlin Academy for 1S.i8 ; and the magnificent work 

 of Haeckel, "Die Radiolarien," Berlin, 1862. 



