This phase in the development of sperm has no counterpart in ovum-development

The correct option is spermiogenesis.

To understand why this is the correct answer, let us break down the phases of gametogenesis (the development of male and female gametes, i.e., spermatogenesis and oogenesis respectively):

1. Phase of Multiplication:
In both spermatogenesis (sperm development) and oogenesis (ovum development), primordial germ cells undergo repeated mitotic divisions to form a large number of gamete mother cells (spermatogonia in males and oogonia in females). Thus, this phase is common to both processes.

2. Phase of Growth:
Spermatogonia and oogonia grow in size by accumulating nutrients to become primary spermatocytes and primary oocytes, respectively. Although the growth phase is much more prolonged and pronounced in oogenesis (due to yolk accumulation), the phase of growth itself is present in both pathways.

3. Polar Body Formation:
This is a feature of oogenesis. During the meiotic divisions of the primary and secondary oocytes, unequal cytoplasmic division occurs, resulting in the formation of polar bodies and a single functional ovum. While this is unique to oogenesis, the question asks for a phase in sperm development that has no counterpart in ovum development.

4. Spermiogenesis:
Once meiosis is complete in spermatogenesis, the resulting cells are haploid, non-motile, spherical cells called spermatids. These spermatids must undergo a highly specialized process of morphological transformation to become functional, motile, flagellated spermatozoa (sperm cells). This differentiation process is called spermiogenesis.
During spermiogenesis, several structural changes occur, including:
- Formation of the acrosome from the Golgi apparatus.
- Condensation and elongation of the nucleus.
- Development of a flagellum (tail) for motility.
- Grouping of mitochondria in the middle piece to provide energy.
- Shedding of excess cytoplasm.

In oogenesis, the completion of meiosis directly yields a functional, non-motile ovum (ootid) that does not need to undergo any such radical metamorphosis or differentiation to achieve its final functional form. Therefore, the transformation phase (spermiogenesis) is entirely unique to sperm development and has no counterpart in ovum development.