Have you ever read Stephen Jay Gould's "The Structure of Evolutionary Theory" Early in the book, beginning on page 10, he writes something very interesting. I'll italicize the most interesting part, which is the last paragraph, and lead into it with a little preliminary portion:

Now such a minimal list of such maximal centrality and importance [he's referring here to the attributes of Darwinianism's central logic, without which the theory could no longer be called Darwinism] bears a description in ordinary language - but its proper designation requires that evolutionary biologists utter a word rigorously expunged from our professional consciousness since day one of our preparatory course work: the concept that dare not speak its name - essense, essence, essence (say the word a few times out loud until the fear evaporates and the laughter recedes). It's high time that we repressed our aversion to this good and honorable word. Theories have essences. (So, by the way, and in a more restrictive and nuanced sense, do organisms - in their limitation and channeling by constraints of structure and history, exressed as Bauplane of higher taxa. My critique of the second theme of Darwinian central logic, Chapters 4-5 and 10-11, will treat this subject in depth. Moreover, my partial defense of organic essences, expressed as support for structionalist versions of evolutionary causality as potential partners with the more conventional Darwinian functionalism that understandable denies intelligibility to any notion of an essence, also underlies the double entendre of this book's title, which honors the intellectual structure of evolutionary theory within Darwinian traditions and their alternatives, and which also urges support for a limited version of structuralist theory, in opposition to certain strict Darwinian verities.

Our unthinking rejection of essences can be muted, or even reversed into propensity for a sympathetic hearing, when we understand that an invocation of this word need not call down the full apparatus of an entirely abstract and eternal Platonic eidos - a reading of "essence" admittedly outside the logic of evolutionary theory, and historical modes of analysis in general. But the solution to a meaningul notion of essence in biology lies within an important episode in the history of emerging evolutionary views, a subject treated extensively in Chapter 4 of this book, with Goethe, Etienne, and Geoffrey St. Hilaire, and Richard Owen as chief protagonists.

After all, the notion of a general anatomical blueprint that contains all particular incarnations by acting as a fundamental building block (Goethe's leaf or Geoffrey's vertebra) moved long ago from the conceptualization as a disembodied and nonmaterial archetype employed by a creator, to an actual structure (or inherited developmental pathway) present in a flesh and blood ancestor - a material basis for channeling, often in highly positve ways, the future history of diversity within particular phylenic lineages.

The paragraph goes on for a few more sentences, dealing mainly with the word "essence", including a remark that the "transcendental morpholigists" had some valid ideas. Not quite FLE, but the mention of a blueprint is very interesting. He is definitely setting up for limitations in structure variation, and apparently the framework that does this is the organism's "essence". Very pedantic writing, though.