Dr. G. C. Wallicli on the ThalassicoUidse. 99 



enables us to distinguisli sucli cliaracters as are normal from 

 those that are accidental or occasional. In this manner Ave 

 discern that the degree of granularity of the endosarc, the 

 number and situation of the sarcoblasts, the colour of the 

 nuclear body, the density of the membranous ectosarc, and (in 

 Collosplicerd) the degree of consolidation of the spherical "shell " 

 are one and all subject to a Avide range of modification ; and 

 hence it follows that any attempt to establish species on 

 distinctions arising out of these characters, unless we could 

 assure ourselves of their having arrived at the same stage in 

 their life-history (a thing which is manifestly impossible), 

 must inevitably lead to misconception. 



Thus in specimens of 8phcerozoum punctatum'^ in Avhicli, 

 owing to the small size of the individuals, it is reasonable to 

 infer that mature groAvth has as yet not been attained, the 

 contents of the membranous capsule appear like a viscid and 

 semitransparent yelloAV fluid, almost devoid of granular par- 

 ticles. The same is observable in young Acanthometrw, and, 

 as I have elsewhere shoAvn, in the last-formed chambers of the 

 Foraminifera and Polycystina. In like manner the ectosarc 

 is more hyaline, and the shafts of the siliceous spicules 

 [acanthostypes)^ although of their full dimensions as to 

 length, are much more slender than in the adult specimens ; 

 Avhilst in specimens of CoUosjyhcera of nearly full size, but 

 in which the appearances just described lead to the infe- 

 rence that they are nevertheless immature, the spherical shell 

 becomes corrugated under pressure, instead of being broken up 

 into fragments, thus rendering it highly probable that many 

 of the spinous and tubular growths met Avith in the shells of 

 that genus may also be dependent on the age of the indiAadual, 

 or varying conditions in the supply of the siliceous material. 



These facts appear to me to be of great importance, inas- 

 much as they are suggestiA^e of the generic unity of Sphcvro- 

 zoum and Collosplimra^ which has already been so strongly 

 indicated by the similarity in the composition and disposition 



* The name " HpliaroT.oum " Avas gh-eu by Mej^en iu 18'U to " a form of 

 agastric animal wliicli he describes as a spherical iiiuco-gelatiuous mass, 

 constituted internally of globules, which, again, consist of A-esicles" (Quar- 

 terly Journal of IMicroscopical Science, veil. \\. p. 78). Assuming the 

 organism thus portrayed to be identical with the ThahtssicoUa ininctata 

 of iiuxley, Miiller retained the name on the plea of prioriti/. The extreme 

 vagueness of Meyen's description, liowever, renders it equally applicable 

 to ThciIassicoUa and numberless "spherical muco-gelatinous masses " to be 

 met with in abundance in the ocean, but which are certainly not members 

 of the Ehizopodal group. The extension of the law of priority to such 

 cases ought, therefore, to be rigidly denied, as holding out a premium to 

 inaccuracy and sloA'enly imestigatiou. 



7* 



