608 Dr. Andrew Wilson [Feb. 4, 



WEEKLY EVENING MEETING, 



Friday, February 4, 1881. 



Thomas Boycott, M.D. F.L.S. Vice-President, in the Chair. 



Dr. Andrew Wilson, F.E.S.E. &c. 



The Origin of Colonial Organisms. 



Every animal develops, directly or indirectly, from an " ovum " or 

 egg, and the plant springs, directly or indirectly, from the germ or 

 seed. One chief difference between low and high forms of life con- 

 sists in the fact that the development of the former ceases at a stage 

 when the development of the latter has barely begun. The Gre- 

 garina is a microscopic speck of protoplasm living parasitically within 

 the bodies of earthworms and other Articulated animals. When 

 development takes place, the body becomes oval, develops a wall or 

 cyst, and the internal protoplasm breaks up into small spindle-shaped 

 masses. The body then ruptures, and the small segments escape, 

 each to become a Gregarina, without further change, save the develop- 

 ment of a nucleus. Each Gregarina at first appears as a single 

 animal or persona, which converts itself by segmentation into an 

 aggregation of such beings. There is thus a temporary development 

 of a compound or colonial state. Similarly the Amoehce (which are 

 low protozoa, living in stagnant water and infusions, and moving as 

 do the white corpuscles of our blood by emitting pseudopodia, or 

 processes of their protoplasmic substance), when undergoing develop- 

 ment, exhibit segmentation or internal division of their substance, 

 and thus exhibit a compound state as a transitory feature of their 

 reproductive phases. 



It is noteworthy that in developing from the egg the embryos of 

 all higher animals exhibit a like process of segmentation or division, 

 as a preliminary phase of their reproduction. There are also forms of 

 protozoa — Myxodictyum — which are truly " colonial " as adults, and 

 which consist of masses of protoplasm aggregated together to form 

 compound organisms. The Foraminifera are likewise " colonial " ; 

 since the shells of these minute protozoa exhibit, as a rule, a division 

 into chambers, each occupied by a distinct protoplasmic unit, organic- 

 ally connected to its neighbours from which it was produced by 

 budding. 



The Volvox glohator, formerly known as the " Globe animalcule," 

 but now ascertained to be a free-swimming lower plant, is composed 

 of distinct units, each provided with two cilia, and resembling a 

 Chlamydomonas. Volvox is, in fact, a colony of monads. A Sponge is 

 a compound or " colonial " organism, in that it consists of an aggre- 



