late 20th and early 21st century critics, Jonathan Wells and Stephen Jay Gould, have objected to the continued use of Haeckel ’ s embryo drawings in textbooks.

Haeckel ’ s illustrations show vertebrate embryos at different stages of development, which exhibit embryonic resemblance as support for evolution, recapitulation as evidence of the Biogenetic Law, and phenotypic divergence as evidence of von Baer ’ s laws.

The series of twenty-four embryos from the early editions of Haeckel ’ s Anthropogenie remain the most famous.

Similarities can be seen along the first two rows ; the appearance of specialized characters in each species can be seen in the columns and a diagonal interpretation leads one to Haeckel ’ s idea of recapitulation.

Haeckel ’ s embryo drawings are primarily intended to express his idiosyncratic theory of embryonic development, the Biogenetic Law, which in turn assumes ( but is not crucial to ) the evolutionary concept of common descent.

Ernst Haeckel, along with Karl von Baer and Wilhelm His, are primarily influential in forming the preliminary foundations of ‘ phylogenetic embryology ’ based on principles of evolution.

The term, ‘ recapitulation ,’ has come to embody Haeckel ’ s Biogenetic Law, for embryonic development is a recapitulation of evolution.

Haeckel portrays a concrete demonstration of his Biogenetic Law through his ‘ Gastrea ’ theory, in which he argues that the early cup-shaped gastrula stage of development is a universal feature of multi-celled animals.

As a response to Haeckel ’ s theory of recapitulation, von Baer enunciates his most notorious laws of development.

Wilhelm His was one of Haeckel ’ s most authoritative and primary opponents advocating physiological embryology.

His ’ depiction of embryological development strongly differs from Haeckel ’ s depiction, for His argues that the phylogenetic explanation of ontogenetic events is unnecessary.

Although Haeckel is proven right about the allantois, the utilization of Krause ’ s embryo as justification turns out to be problematic, for the embryo is that of a bird rather than a human.

In response to Haeckel ’ s evolutionary claim that all vertebrates are essentially identical in the first month of embryonic life as proof of common descent, His responds by insisting that a more skilled observer would recognize even sooner that early embryos can be distinguished.

Haeckel ’ s opponents believe that he de-emphasizes the differences between early embryonic stages in order to make the similarities between embryos of different species more pronounced.

Although Rutimeyer did not denounce Haeckel ’ s embryo drawings as fraud, he argued that such drawings are manipulations of public and scientific thought.

As a pioneer in mammalian embryology, he was one of Haeckel ’ s strongest critics.

Nevertheless, Bischoff ’ s main argument was in reference to Haeckel ’ s drawings of human embryos, for Haeckel is later accused of miscopying the dog embryo from him.

Throughout Haeckel ’ s time, criticism of his embryo drawings was often due in part to his critics ' belief in his representations of embryological development as “ crude schemata .” In this way, Haeckel specifically selected relevant features to portray in his drawings.

Haeckel ’ s opponents found his methods problematic because such simplification eliminates certain structures that differentiate between higher and lower vertebrates.

In 1877, Rudolf Virchow ( 1821 – 1902 ), once an inspiration to Haeckel at Würzburg, proclaimed that Haeckel ’ s embryo drawings represent mere hypotheses.

Although the early embryos of different species exhibit similarities, Haeckel apparently exaggerated these similarities in support of his Recapitulation theory, sometimes known as the Biogenetic Law or " Ontogeny recapitulates phylogeny ".

Despite the numerous oppositions, Haeckel has influenced many disciplines in science in his drive to integrate such disciplines of taxonomy and embryology into the Darwinian framework and to investigate phylogenetic reconstruction through his Biogenetic Law.

Haeckel advanced a version of the earlier " recapitulation theory ", previously set out by Étienne Serres in the 1820s and supported by followers of Geoffroy including Robert Edmond Grant, which proposed a link between ontogeny ( development of form ) and phylogeny ( evolutionary descent ), summed up by Haeckel in the phrase " ontogeny recapitulates phylogeny ".

The debate between Haeckel and His ultimately becomes fueled by the description of an embryo that Wilhelm Krause propels directly into the ongoing feud between Haeckel and His.

The underlying debate between Haeckel and His derives from differing viewpoints regarding the similarity or dissimilarity of vertebrate embryos.

In determining the relationships between " phylogenetic linkages " and " evolutionary laws of form ," both Gegenbaur and Haeckel relied on a method of comparison.

For example, Haeckel proposed that the pharyngeal grooves between the pharyngeal arches in the neck of the human embryo resembled gill slits of fish, thus representing an adult " fishlike " developmental stage as well as signifying a fishlike ancestor.

Haeckel produced several embryo drawings that often overemphasized similarities between embryos of related species.

Early attempts to identify relationships between major groups were made in the 19th century by Ernst Haeckel, and by comparative anatomists such as Thomas Henry Huxley and E. Ray Lankester.

Nevertheless, his chief interest was in human evolution, influenced by Ernst Haeckel, who reasoned that there must be intermediate species between apes and human.

Extensive correspondence exists between Müller and Darwin, and Müller also corresponded with Hermann Müller, Alexander Agassiz, Ernst Krause and Ernst Haeckel.

Romanes ' 1892 copy of Ernst Haeckel's allegedly fraudulent embryo drawings ( this version of the figure is often attributed incorrectly to Haeckel ).

In addressing his embryo drawings to a general audience, Haeckel does not cite any sources, which gives his opponents the freedom to make assumptions regarding the originality of his work.

Ultimately, His goes so far as to accuse Haeckel of “ faking ” his embryo illustrations to make the vertebrate embryos appear more similar than in reality.

Rutimeyer claimed that Haeckel “ had taken to kinds of liberty with established truth .” Rutimeyer claimed that Haeckel presented the same image three consecutive times as the embryo of the dog, the chicken, and the turtle.

Romanes's 1892 copy of Ernst Haeckel's controversial embryo drawings ( this version of the figure is often attributed incorrectly to Haeckel ).

Ernst Haeckel ( 1866 ), in his endeavour to produce a synthesis of Darwin's theory with Lamarckism and Naturphilosophie, proposed that " ontogeny recapitulates phylogeny ," that is, the development of the embryo of every species ( ontogeny ) fully repeats the evolutionary development of that species ( phylogeny ), in Geoffroy's linear model rather than Darwin's idea of branching evolution.

The presence of gill-like slits in the neck of the developing human embryo famously led Ernst Haeckel to postulate that " ontogeny recapitulates phylogeny "; this hypothesis, while false, contains elements of truth, as explored by Stephen Jay Gould in Ontogeny and Phylogeny.

Haeckel promoted and popularized Charles Darwin's work in Germany and developed the controversial recapitulation theory (" ontogeny recapitulates phylogeny ") claiming that an individual organism's biological development, or ontogeny, parallels and summarizes its species ' evolutionary development, or phylogeny.

Haeckel introduced the concept of " heterochrony ", which is the change in timing of embryonic development over the course of evolution.

Haeckel proposes that all classes of vertebrates pass through an evolutionarily conserved “ phylotypic ” stage of development, a period of reduced phenotypic diversity among higher embryos.

Haeckel argues that certain features in embryonic development are conserved and palingenetic, while others are caenogenetic.

Haeckel was not the only one to create a series of drawings representing embryonic development.

Karl E. von Baer and Haeckel both struggled to model one of the most complex problems facing embryologists at the time: the arrangement of general and special characters during development in different species of animals.

Haeckel encountered numerous oppositions to his artistic depictions of embryonic development during the late nineteenth and early twentieth centuries.

Haeckel then provided a means of pursuing this aim with his biogenetic law, in which he proposed to compare an individual's various stages of development with its ancestral line.

For Haeckel, language specifically represented the concept that all phenomena of human development relate to the laws of biology.

" Haeckel ’ s ABC of evolution and development.