Embryology in the Holy Qur’ān: A segmented body like a Leech

A leech’s body is organised into repeating units called segments which gives rise to a ringed appearance of the body hence the name “ringed worms ”38

Figure 9 Human embryos during the fourth
week, approx. 21-25 days. Note the
segments or somites and the leech-like
appearance of the embryos. (From Larsen,
William J., Human Embryology, 2nd ed.,
Churchill Livingstone, Inc., 1997, p. 75).

The human embryo is also segmented just like a leech or worm as Professor Peter Nathanielsz describes in A Time to be Born: The Life of the Unborn Child:

By the end of the third week the embryo has undergone segmentation, rather like an earth worm, and now consists of zones like stacked circular tires. Each segment will give rise to a different part of the body's long axis. The repetition of structures in segments is best seen in the chest. There, each vertebra and the attached rib is produced from one embryonic segment.39

The segments of the embryo consist of somites (Figure 9), cell masses which develop into ribs, vertebrae and back muscles:

Somites are bilaterally paired blocks of mesoderm that give the embryo a segmented appearance... Somites begin to appear by day 20, and number 42-44 pairs by day 35. Beginning in week 4, each somite subdivides into three tissue masses: a sclerotome, which surrounds the neural tube and gives rise to bone tissue of the vertebral column; a myotome, which gives rise to muscles of the trunk; and a dermatome, which gives rise to the dermis of the skin and to its associated subcutaneous tissue.40

The gut like a “straight tube”
The third week is characterized by the development of the three germ layers followed by the formation of three important structures (the primitive streak, the notochord, and the neural tube).

During development, cells form three germ layers: the ectoderm is the outer most layer, the mesoderm is the middle layer, and the endoderm is the innermost layer.


38 Garwood and Campbell (2007).
39 Nathanielsz (1994, p. 22). Peter W. Nathanielsz is a Professor at the Laboratory for Pregnancy and Newborn Research, Cornell University, Ithaca, USA. “Professor Nathanielsz was amongst the handful of pioneers who assisted at the birth about thirty years ago of the new discipline of fetology and has remained at the forefront of what is now an enormous field. His laboratory has contributed many of the technical advances that now allow the most intimate details of fetal life to be examined with a precision equal to that of a cosmologists’ radio-telescope.” (ibid, vii).
40 Saladin (2007, p. 114).

Figure 10 A diagrammatic representation showing the relative positions of the three germ layers and their derivatives. The enteron and coelom form the gut and body cavities, respectively. The ectoderm forms the central and peripheral nervous systems, as well as skin cells (epidermis). The mesoderm forms many essential organs, including bone, blood, heart, spleen, and kidneys. The endoderm forms the remaining organs, as well as the digestive and respiratory tracts. (From Ted Zerucha, Human Development, 1999, page 53).

These three germ layers give rise to all the tissues and organs of the embryo (Figure 10). These layers curl to form a tube-like structure which Anthony Smith, in The Human Body, also likens to a worm:

There are three layers much like a cake with filling in the middle. These three layers then curl to form a tube. The early embryo is like a worm, with a gut running from one end to the other, an outer covering also running from end to end and a central layer filling the space between the two.41

Ted Zerucha in Human Development also describes the gut of the embryo as a tube:

If one imagines what a cross section through a human body looks like in a very general sense, it would likely resemble something similar to that shown in [Figure 10]. Running through the body, along the anterior-posterior axis, is the gut. The gut is essentially a tube that runs from the mouth, through the digestive system, to the anus.42

The tube-like depiction of the embryo’s gut is not unlike that of an annelid as described in The Columbia Encyclopedia:

The digestive system of annelids consists of an unsegmented gut that runs through the middle of the body from the mouth, located on the underside of the head, to the anus, which is on the pygidium [the posterior terminal region]. 43

41 Smith (1998, p. 38).
42 Zerucha (2009, p. 52).
43 “Annelida” in The Columbia Encyclopedia (2008).