egg and dart

...The stories of geese or chickens that lay golden eggs, which are told in folk tales and legends, are deeply connected to these beliefs, and it is said that golden eggs represent the sun and silver eggs represent the moon. Also, in Greek architecture, there is a repeating pattern called "egg and dart" that is said to symbolize the female and male reproductive organs or hermaphroditism by combining eggs and arrowheads. [Aramata Hiroshi]
[Eggs and the Japanese]
The reason it is also written as "tamago" is thought to come from its round shape, but it may also be because it was thought to contain a soul (tama).

*Some of the terminology that mentions "egg and dart" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…民話や伝説に語られる金の卵を産むガチョウまたはニワトリの話は，これらの信仰に深くかかわっており，金の卵は太陽，銀の卵は月をも表すといわれている。またギリシア建築の装飾に〈卵鏃（らんぞく）飾りegg and dart〉と称する繰返し模様があり，卵と鏃（やじり）の組合せで女と男の生殖器，あるいは両性具有を象徴するといわれる。【荒俣 宏】
【卵と日本人】
　玉子とも書くのは形が丸いところからきたと思われるが，魂（たま）の入ったものと考えたためとも解される。…

※「egg and dart」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報