194 



cell must elaborate monocytic ingestive organs apart from locomotor or- 

 gans, as in the solitary Protozoa; whereas if we assume that the mono- 

 cytic differentiation ceases in favour of polycytic, then each cell will 

 differentiate in time and not in space, will lose flagella when ingestion 

 is effected and Avill, in accordance with the principles of polycytic 

 differentiation migrate inwards from the locomotor area''. Thus each 

 cell will perform in its turn the function of locomotion and ingestion 

 and later, digestion. In fact, in this multicellular colony, there will 

 be no division of labour between the cells, but each cell will play 

 many parts. This stage may be compared to the stage of monocytic 

 differentiation exemplified by Amoeba, the functions of locomotion 

 and of ingestion being diffused. Just as in Amoeba, locomotion of the 

 whole brings the outer part of the organism in contact with the food 

 particles which are then ingested to the interior of the organism, so 

 in this colony the whole individual moves into contact with food par- 

 ticles and these are transferred to the interior preparatory to digestion. 

 The processes effected by the general contractility of the protoplasm 

 in the one case are accomplished in the other by the activity of indi- 

 vidual cells. 



It will be observed that, in this case, each cell performs a series 

 of functions, and is also polymorphic, the flagellum being contracted, 

 and the amoeboid phase being assumed. 



Such a colony has yet to be described in full, but in most points 

 it is closely approached by Proterospongia [Savillia] ^^. The ingestive 

 process is not described in this form, but the cells are undoubtedly 

 polymorphic in that in connection with the sexual process, immigra- 

 tory flagellated cells become amoeboid. 



The ingestive processes in sponges, at any rate in the simpler 

 forms, are precisely of this nature. In Gratitia^^ for example the 

 flagellated cells, upon being charged with food particles, withdraw 

 their flagella, and becoming amoeboid, migrate into the so-called 

 »mesoderm«. We thus find that Proterospongia illustrates such a low 

 form of organism as we have mentioned, and in the sponges are to be 

 found ingestive processes, dependent upon polymorphism of the cells, 

 precisely similar to those suggested as primitive in the hypothetical 

 multicellular colony 12. 



9 This migration inwards is dependent upon the same laws as cause a food 

 particle to migrate to the interior of Amoeba. 



w W. S. Kent, Month. Micro. Journ. Vol. VI. 1871. 



11 This migration has recently been stigmatised as »pathological«. The objec- 

 tion was to some extent forestalled in my paper. Annalsof Mag. Nat. Hist. Vol. XIII. 



12 »It appears to me not impossible that the Coelenterata may have had an 

 ancestor in which a digestive tract was physiologically replaced by a solid mass 

 of amoeboid cells«. F. M. Balfour. Comp. Embr. Vol. I. p. 178, 



