386 Mr. Weaver's View o/' Ehrenberg's Observatio?is 



often resembles an Ammonite or Nautilus, being considered 

 as the internal bone. On the other hand, at a later period, 

 M. Dujardin denied that these animals possessed any organic 

 structure, stating that they consisted simply of an animated 

 slime capable of extension, encased by an indurated external 

 shell, and associating them with the pseudopodian Amoeba 

 of the Infusoria. Dr. Ehrenberg now further demonstrates, 

 by figures and descriptions, their true organic structure, thus 

 fully establishing his former positions, both as to simple Po- 

 lythalamia and Polythalamia forming Polyparies. He proves 

 that they are not internal bones, but external shells encasing 

 a soft body, the shell being perforated, as it were, in all parts 

 by numerous pores, from which the animal projects long fila- 

 ments, capable at will of extension, retraction and bifid divi- 

 sion, and productive of locomotion. The author further ob- 

 serves: M. Dujardin has, in August 1840, presented to the 

 Paris Academy a Memoire sur urie Classification des InJ'usoires 

 en rapport avec leur organisation!^ in which a new arrangement 

 of the Infusoria is exhibited, and in this the Polythalamia are 

 again introduced as Rhizopodes in association with Amoeba and 

 Actinophrys of the Infusoria, forming a separate family. If, 

 however, anatomical and physiological details are to be taken 

 into account when we proceed to the systematic arrangement 

 of different organic bodies, and we are not governed merely 

 by the relations of external forms, M. Dujardin's arrangement 

 cannot be deemed a happy one. He has in no case shown a 

 polygastric structure in the Rhizopodes, and that it is not po- 

 lygastric is proved anew by my investigations now commu- 

 nicated. 



It has been shown in a former part of this paper that Dr. 

 Ehrenberg had recognized six species of Infusoria in the chalk 

 formation, so closely resembling living species as not to be di- 

 stinguished from them, and hence he was led to give to them 

 the same names; namely, Eunotia Zebra, Fragilaria rhabdo- 

 soma, Fragilaria striolata P, Gallionella aurickalca, Navicula 

 ventricosa, and Synedra ulna. He had also referred, with a 

 mark of interrogation, the following four species of calcareous- 

 shelled Polythalamia to the white chalk, in which they are 

 very extensively distributed, namely, Globigerina bulloides, 

 Globigerina helicina, Rosalina globularis, and Textilaria aci- 

 culata, all of which were stated by M. d'Orbigny to have oc- 

 curred in the living state only in the Adriatic Sea and the 

 Ocean. If any doubt had existed as to the identity of all these 

 fossil and living species, it has been completely removed by 

 the later researches of Dr. Ehrenberg, by which the actual 

 number of known species found in the chalk formation and in 



