D.— ZOOLOGY. 65 



from the flagellates, we owe our sense of time ; so that our appreciation of 

 dancing, poetry, and music shows that we are still flagellates at heart. 



How was the transition from flagellate to multicellar organism effected ? 

 And what advantage did it bring ? We have seen that a flagellum beats 

 continuously and that a flagellate divides longitudinally. We must now 

 turn our attention to a third cardinal characteristic — that flagellates exude 

 on their exterior a watery jelly which is sticky. 18 



It seems at first sight a trifling detail of natural history to mention 

 that flagellates exude a transparent mucilaginous substance which coats 

 them, thinly if they swim, and thickly if they stay still for it to accumulate. 

 Yet to this one property is due, not only their first aggregation into multi- 

 cellular masses, but the possibility of all the physiological developments 

 in plants, sponges, and metazoa, of which up to the present day those 

 masses have shown themselves capable. Church said that in the primitive 

 unit of protoplasm the peripheral deposit of waste carbohydrate is a 

 necessary condition of its metabolism, but culminates in the production 

 of the timber-tree. I would add, that it culminates also in the production 

 of the mammal. 



That an adhesive surface will enable flagellates to cohere is obvious ; 

 this, with the repeated longitudinal fission of the cells, produces first the 

 temporary cohesion of rapidly dividing monads, which are the product 

 of the encysted flagellate, and are gametes — exactly comparable with those 

 of the sperm-tassels of Lumbricus ; where the asexually produced genera- 

 tion of the earth-worm is a flagellate, dividing longitudinally, and ad- 

 hering to its brethren, so as to resemble a piece of floating columnar ciliated 

 epithelium. In the earth-worm's spermatozoa, as in most flagellates, 

 the coherence is only temporary and the ultimate product of the longi- 

 tudinal division is a free-swimming gamete. But in many flagellates — 

 in members of almost every group of flagellates — as a method of distribu- 

 tion the original products of division never separate, and with repeated 

 longitudinal fission the swimming sheet of cells becomes larger and larger, 

 and therefore swims faster. Almost always, however, it becomes convex 

 on the flagellate side — possibly because there the continuity of the water- 

 jelly surface is broken by the moving bases of the flagella — but there is 

 clearly no a priori reason to expect surface tensions to be equal in the 

 dissimilar flagellate and non-flagellate surfaces. The phenomena show 

 that the surface tension of the flagellate surface is the less, so that it 

 becomes increasingly convex, until the growing sheet of cells is bent 

 round into a hollow sphere, such as we admire in Volvox, Synctypta, 

 Uroglenopsis, &c. 



Thus the properties of longitudinal fission and gelatinous exudation 

 give rise in all flagellate groups to a secondary characteristic of the flagellates, 

 their tendency to form hollow spheres bounded by a single layer of cells. 



18 Church, I.e. p. 8, considers that because the supply of CO., is disproportionally 

 large compared with that of the other ingredients of protein, there is a general excessive 

 synthesis of CHOH compounds, followed by their elimination on the periphery of tbe 

 cell as mucilage or ' wall ' deposits. See E. Bresslau, 1924, ' Neues iiber Tektin ' : 

 Verh. Deutsch. Zool. Ges., E.V. xxix, p. 91. He finds the slime on Colpidiurn to be 

 mucin ; see also Bresslau, 1924, Senckenbergischen Naturf. Ges. p. 49, and G. Lapage, 

 1925, Q.J.M.S. ; also see Q.J.M.S. 1895, p. 22, and p. 14, Fig. (a). 



1927 F 



