1873.] the Invertebrata in relation to Evolution. 



221 



cells, having a tolerably distinct membraniforni wall and a conspicuous 

 round central nucleus, thus corresponding closely with the Gregarina 

 type." I might mention in passing that, having frequently taken in 

 the towing-net the unequivocal allies of Dictyocha with sarcode bodies 

 identical with those of Sj^icerozoum, I have no hesitation in assuming 

 Dictyocha itself to belong rather to the Thalassicollidse than to the group 

 with which it is more usually associated. This family is commonly 

 included under the head of Phizopoda ; and there can be no doubt that 

 the generalization, irrespective of that term, is a correct one ; but it is a 

 stretch of transcendental anatomy to speak of the existence of pseudo- 

 podia in any member of it. The radiating branched filaments within the 

 dense external investment of Thalassicolla nucleata are not extensions of 

 the sarcode-body, like those of Gromia for example, but apparently act as 

 retinacula, and as conduits for dialytic currents, which may account for 

 the phenomenon of cyclosis observed in some instances. 



Professor James-Clark, of Pennsylvania, appears to have satisfied him- 

 self, at least, that there is a remarkable agreement of characters exhibited 

 between the Porifera and the Infusoria, which are connected, as he 

 endeavours to show, by a regular gradation of animals. The derivation 

 of the latter group of Protozoa from the former, which I had myself 

 assumed quite independently, is therefore supported by that gentleman's 

 researches. 



Even with our present advanced knowledge of the Infusoria it is 

 doubtful if we do not still include amongst them the larva) of Turodlaria; 

 and, indeed, the passage from the one type to the other would appear to 

 be natural and easy. On the other hand, tracing through such forms as 

 NemerUs, Bonellia, and Pricipulus, Svpunculw will lead directly to the 

 less equivocal Echinodermata ; and here the series must wind up, for 

 further evolution, though perhaps possible, does not appear to have 

 taken place. 



The existence of such low or simple forms of Potifera as the genus 

 Asplanchna, for example, would be favourable to the idea that the 

 NoctilucidaB might have been the progenitors of that order of beings. It 

 is of course quite gratuitous, but convenient, at present to assume that 

 the Noctilucidae would thus hold the same relationship to the Polycystina 

 that the Infusoria appear to do to the Porifera. However this may be, 

 it is more certain that the Potifera are at the root of the annulose and 

 articulate series. 



Prom the Eotifera, through the Annelida, we may thus trace the de- 

 velopment of the crustaceous and chitinous types of Articulata like a 

 dichotomous branch. 



The Annelida may be linked with the Crustacea by means of the 

 SagittidsB, whose exquisitely striped muscular fibres accord to them a 

 higher position than the other parts of their organization would perhaps 

 warrant them to take. 



