Ryder.] 1 ^^ [April 7, 



bryonic form is also modified. lu so far as such statical interference 

 affects the figure of the organism tliej'^ are morphogenetic or form-deter- 

 mining. In so far the figure of a developing being is disturbed or modi- 

 fied by statical agencies its figure may be said to be subject to statogenetic 

 inrtuences. No existing larval form lias escaped the influence upon its 

 own shape of a constantly active statical etiuilibrium of its own substance. 

 There is, therefore, a constant struggle going on during development be- 

 tween the pliylogenetic and ontogenetic forces, determining the sequence 

 and relations of the successive cleavages of the egg and the statical equi- 

 libria that obtain amongst its several parts. Statogenetic processes are, 

 therefore, as constant and universal as the pliylogenetic and ontogenetic. 

 One may even go so far as to say that possibly the relations thus tending 

 to be established by statical conditions may tend to become transmissible 

 as hereditary tendencies. Such indeed is the view upheld by Prof. E. B. 

 Wilson in his remarkable paper on "The Cell-lineage of Nereis." * I have 

 myself seen no less than three consecutive recurrences of the same stati- 

 cal conditions in a fish egg, none of which can, for this reason, be defi- 

 nitely proved to be purely ontogenetic. 



The lacetted eyes of insects are usually hexagonal, but not invariably 

 so. I have found triangular, quadrangular and hexagonal fjicets in the 

 eyes of Tachinus. Now these different forms are due to disturbances of 

 the statical conditions obtaining between the individual ommatidia during 

 growth of the eye. If the pressure is the same from every direction lat- 

 erally during growth, a cylindrical eye w^ould result. It the lateral pres- 

 sure is the same from six points at equal distances apart around each e5'e, 

 tlie regular hexagon will result; should any two opposite pairs of the six 

 pressures be less than tlie pressures from the other two pairs irregularities 

 in the hexagons'will appear. If cylinders are grouped so that the side of 

 every one touched the sides of six others, which may be done by bringing 

 their tops into rows in three directions, and if now each cylinder be in- 

 creased in diameter, there will be pressure developed in six directions 

 diverging at equal angles of 60° from one another, a hexagonal configura- 

 tion of tlie ends of the cylinders would ultimately result, provided thsy 

 were formed of plastic material. The same thing sometimes happuns 

 when a plastic and nearly homogeneous mass cools and contracts, when 

 cracks appear in the mass generally dividing it into pentagonal and hex- 

 agonal prisms, as happened in case of the cooling of intruded mass of 

 molten basalt in the Giant's Caus^eway in Ireland. A series of cylinders 

 arranged so that every one shall touch six others is also most economical 

 of space, and in the processes of growth is the natural result of a statical 

 equilibrium due to equal pressure from six directions in a plape. If a 

 series of cylinders be brought into rows in two directions only, and so as 

 to touch tlieir neighbors at only four points, quadrangular columns would 

 result were the diameter of every cylinder increased against four others, 

 provided all were composed of plastic material. In these ways have the 



* Journ. Morphology, Vol. vi. 



