One of the central, unresolved controversies in biology concerns the distribution of primitive versus advanced characters at different stages of vertebrate development. This controversy has major implications for evolutionary developmental biology and phylogenetics. Ernst Haeckel addressed the issue with his Biogenetic Law, and his embryo drawings functioned as supporting data. We re-examine Haeckel's work and its significance for modern efforts to develop a rigorous comparative framework for developmental studies. Haeckel's comparative embryology was evolutionary but non-quantitative. It was based on developmental sequences, and treated heterochrony as a sequence change. It is not always clear whether he believed in recapitulation of single characters or entire stages. The Biogenetic Law is supported by several recent studies -- if applied to single characters only. Haeckel's important but overlooked alphabetical analogy of evolution and development is an advance on von Baer. Haeckel recognized the evolutionary diversity in early embryonic stages, in line with modern thinking. He did not necessarily advocate the strict form of recapitulation and terminal addition commonly attributed to him. Haeckel's much-criticized embryo drawings are important as phylogenetic hypotheses, teaching aids, and evidence for evolution. While some criticisms of the drawings are legitimate, others are more tendentious. In opposition to Haeckel and his embryo drawings, Wilhelm His made major advances towards developing a quantitative comparative embryology based on morphometrics. Unfortunately His's work in this area is largely forgotten. Despite his obvious flaws, Haeckel can be seen as the father of a sequence-based phylogenetic embryology.
No abstract
Paraffin histology is one of the most important and commonly-used laboratory techniques in diagnostic histopathology. The discovery of paraffin embedding is often attributed to the pathologist Edwin Klebs. Klebs was following the lead of Stricker, who embedded embryos in a mixture of hot stearin and white beeswax. We show that Klebs experimented with paraffin wax for embedding tumour tissue. But he quickly rejected it as unsuitable because paraffin wax did not infiltrate the tissue. One of Klebs’ correspondents, embryologist Wilhelm His, Sr., learned of Klebs’ experiments and decided to try paraffin embedding. His dehydrated chicken embryos in alcohol, cleared them in lavender oil, and dripped hot paraffin wax onto them. This process allowed His to cut good sections. Here, we have replicated His’s paraffin embedding protocol in order to determine whether His had indeed made the landmark discovery of infiltration embedding with paraffin wax. We followed the protocol that he gives in his 1868 monograph on the early development of the chicken. The protocol described by His failed, in our hands, to yield sections of the quality that he illustrates in his monograph. Typically, the tissue disintegrated when sectioned due to poor infiltration of the wax. Usable sections could only be obtained if His’s protocol was modified by melting the embedded embryos in fresh paraffin wax. One explanation for our findings is that we failed to faithfully replicate His’s protocol. Another is that his protocol was incomplete. We suggest that His is likely to have discovered and perfected infiltration embedding with paraffin wax but did not publish a complete protocol.
ZusammenfassungDie paraffinbasierte histologische Untersuchung ist eines der wichtigsten angewendeten Laborverfahren in der diagnostischen Histopathologie. Die Entwicklung der Paraffineinbettung wird oft dem Pathologen Edwin Klebs zugeschrieben. Klebs orientierte sich an den Arbeiten von Stricker, der Embryonen in eine Mischung aus heißem Tristearin und weißem Bienenwachs einbettete, und experimentierte mit Paraffin, um Tumorgewebe einzubetten. Er verwarf den Ansatz aber rasch, da Paraffin das Gewebe nicht infiltrierte. Klebs stand im Briefwechsel mit dem Embryologen Wilhelm His Senior, der von dessen Experimenten erfuhr und beschloss, sich an der Paraffineinbettung zu versuchen. His entwässerte Hühnerembryonen in Alkohol, klärte sie mit Lavendelöl und träufelte heißes Paraffin darüber. Dieses Verfahren ermöglichte ihm die Anfertigung guter Schnitte. In der vorliegenden Arbeit haben wir His’ Protokoll der Paraffineinbettung nachvollzogen, um zu ermitteln, ob His tatsächlich die Infiltrationseinbettung mit Paraffin gelungen ist. Wir befolgten das Protokoll aus seiner 1868 erschienenen Monografie. Anhand der Anweisungen von His gelang es uns nicht, Schnitte mit der von ihm illustrierten Qualität herzustellen. In der Regel zerfiel das Gewebe beim Schneiden wegen schlechter Wachsinfiltration. Brauchbare Schnitte wurden nur bei Abwandlung von His’ Protokoll durch das Wiedereinschmelzen der eingebetteten Embryos in frischem Paraffin erreicht. Möglicherweise ist es uns nicht gelungen ist, das Protokoll von His detailgetreu zu replizieren, oder das Protokoll war unvollständig. Nach unserer Einschätzung hat His wahrscheinlich die Infiltrationseinbettung mit Paraffin erfunden und perfektioniert, aber kein vollständiges Protokoll veröffentlicht.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.