Mr. T. H. Huxley on the genus Thalassicolla. 441 



tered through the substance, larger in the external zone, smaller 

 and more irregular in the interior. 



If the animal is much compressed, nuclei and nucleated cells 

 are forced out from its interior. 



Finally, two specimens of Actinophrys have been observed to 

 fuse together and become one. 



It is unnecessary to point out the perfect analogy between 

 Actinophrys and Thalassicolla nucleata, with one exception, that 

 the large internal cell was not observed in Actinophrys — a cir- 

 cumstance which might readily occur if it were delicate, even 

 though it existed. 



The argument derived from this analogy becomes still more 

 strengthened if we turn to the excellent account of Noctiluca — 

 a marine phosphorescent body which has long been a zoological 

 puzzle — by M. de Quatrefages. For the details I must refer to 

 that observer's paper in the ( Annales des Sciences/ but I may 

 state that its structure is essentially similar to that of Thalassi- 

 colla nucleata, supposing that the latter had given exit to its 

 central cell by a depression at one point of its surface. Nocti- 

 luca however appears to feed after the manner of Actinophrys, 

 and perhaps conjugates also, as M. de Quatrefages " has met 

 with double individuals two or three times." This he considers 

 an evidence of spontaneous fission ; but further observation might 

 have reversed this judgement, as it did that of Kolliker with 

 regard to Actinophrys. 



From the invariable adhesion of grains of sand to one part of 

 the surface of Noctiluca, it would seem to be set free from some 

 unknown fixed form which is probably analogous in its structure 

 to Thalassicolla punctata. 



To sum up the different lines of argument it may be said — 



1. That the Thalassicolla punctata is not an exceptional form 

 of animal life, but belongs to the same great division as the 

 Sponges, Foraminifera, Infusoria, and Gregarinidse, — the Pro- 

 tozoa or unicellular animals. 



2. That the Protozoa have definite characters as a class, which 

 are — 



a. That they are either simple nucleated cells or aggre- 

 gations of such cells, which are not subordinated to a 

 common life. 



b. That they have a mode of reproduction consisting in an 

 endogenous development of cells, preceded by a process 

 analogous to the conjugation of the lower plants. 



3. That the Thalassicolla nucleata closely resembles Actino- 

 phrys Sol, which is known to conjugate, and which there is great 

 reason to believe is the reproductive stage of one of the Vorti- 

 cellinse. 



