Although he did not idealize his figures, most of Wilson’s figures in Cell-Lineage are not exact copies of what he was seeing through the microscope. With the exception of a handful, every figure is a composite image in some way, meaning that Wilson was piecing them together either mentally or manually. Wilson’s figures consist of two kinds of composites images: composites made up of observations from different specimens and composites of those from the same specimen. It is likely that these composites were constructed by combining several camera lucida sketches together, which would explain in part how Wilson got ninety-two final figures from hundreds of sketches.
The first kind of composite, that consisting of observations of different embryos, is more rare and Wilson doesn’t specifically indicate which figures are of this kind. “Most of the figures were drawn from a single specimen,“ he states, “but in a few cases, in order to economize space, a single figure combines the sketches from more than one specimen.” (Wilson 1892). These composite images were also likely created due to the difficulty of studying all parts of a single embryo at any one moment, especially those at more advanced stages. This is one of the reasons why Wilson needed a large number of embryos and why he used a combination of fixed and live embryos to make his observations and to produce drawings for his figures. While live embryos provided a more accurate view of development, fixed specimens were easier to observe and draw from (Wilson 1892). Because time no longer is a factor when looking at fixed specimens, they can be more carefully studied and can be referred back to, revealing structures or phenomena that may have been overlooked in the live embryo.
The second kind of composite image, made up of observations from the same embryo, applies to almost every figure with the exception of a handful. Although Wilson makes little mention of this, interaction with any compound microscope will demonstrate that when looking at a three-dimensional object, only structures in the same plane can be viewed at any one time. Especially when using higher objectives, to get a sense of the dimensionality of the embryo, one has to turn the focus knob to move through the different focal planes. Only when taken all together does the three-dimensionality of the entire embryo become apparent.
Many of Wilson’s images clearly show multiple planes of detail, meaning he must have had some method of stitching them together, whether mentally or by superposing multiple drawings. This phenomenon is most clearly demonstrated by Wilson’s figures that display an “optical section,” or a single focal plane (Figs. 18, 34, 71 below) and one that he states is a composite of a surface view on top and an optical section on the bottom (Fig. 70 below). Today, this dimensionality can be achieved automatically by constructing z-stacks, stacks of consecutive photographs of different focal plants, which can then be digitally stitched together. But during Wilson’s time, a view of the whole in-focus embryo had to be mentally and manually composed.