卵の形が「ゼロ」（０）の形に似ているからであろう。
Sentence Analyzer
English Translation
The shape of an egg is like the shape of a naught (0).
Furigana
Romanji
Tamago no katachi ga" zero" zero no katachi ni niteiru kara de arou.
Words
卵
(たまご)
eggs; egg; spawn; roe; hen egg; (an expert) in the making; beginning; origin; infancy
の
(の)
indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question
形
(かたち、よう)
form; shape; figure; visage
が
(が)
indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and
零
(れい、ぜろ、ゼロ)
zero; nought
○
(まる)
circle (sometimes used for zero); 'correct' (when marking); symbol used as a placeholder (either because a number of other words could be used in that position, or because of censorship); period; full stop; maru mark; semivoiced sound; p-sound
に
(に)
at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although
似る
(にる)
to resemble; to look like; to take after; to be similar (in status, condition, etc.); to be close; to be alike; to be like
から
(から)
from (e.g. time, place, numerical quantity); since; from (originator); by; because; since; out of (constituent, part); through (e.g. window, vestibule); after; since
だ
(だ)
be; is; indicates past or completed action; indicates light imperative
或
(ある)
a certain ...; some ...