Tag: introduction to reproduction

In all terrestrial vertebrates except the placental mammals, the genital ducts and excretory ducts, open into the cloaca. In mammals, however, the cloaca becomes separate into a dorsal part, which conveys the faeces and a ventral part, which receives excretory and genital products. The sperm cells from seminiferous tubules pass into Bidder's canal through vasa efferentia. The Bidder's canal runs along the length of each kidney near its inner side. Thus, vasa efferentia conduct mature sperm from testis to the ureter.

Eggs laid by female frogs are protected by Gelatinous material that prevents desiccation of the developing embryo.

Tympanum is a membrane of the eardrum. It has a three chambered heart made of muscle tissues. The body of the frog is divisible into head and trunk. The head is in a triangular shape. The lungs is present in the trunk of the body.

Tadpole larva has a rudimentary mouth which is not highly developed. Thus frog tadpole is a herbivore, feeding on relatively simpler food found available in the aquatic systems, such as Zooplanktons. Upon growth, tadpole larva undergoes metamorphosis where the mouth and internal organs will be rearranged to develop an adult carnivorous lifestyle.

The oviducts present in amphibians are simple tubes which are lined with glands that produce mucus and jelly. Oviducts in male frogs are vestigial oviducts as they have no specific function and no role in reproduction. However, in female, oviduct responds to ovarian or female sex hormones by enlarging and acquiring a lumen. Oviducts carries egg to the cloaca. This posterior opening is the common exit for intestinal, urinary and reproductive tracts. The oviduct of the female is known as the rudimentary oviduct or Mullerian duct. This duct has no lumen and is very much reduced in size. Due to small size, it is difficult to locate these ducts. 

• The larva of Herdmania shows retrogressive metamorphosis in which the larva looses the characters of chordates and attains the form of a invertebrate.
• The tadpole larva of Frog shows fish like characters like gills, gill slits and lateral line organs. This indicates that amphibians evolved from fish like ancestors.
• Gingko is a primitive gymnosperm. Presence of flagellated sperms in Gingko like in Pteridophytes suggest that gymnosperms have evolved from Pteridophytes.

In male frogs, each testis is located on the anterio-ventral margin of the kidney. From each testis, ten to twelve vasa efferentia emerge and enter the kidney to open into the Bidder's canal. The Bidder's canal helps in the transfer of sperms via the vasa efferentia. Vasa efferentia open into the Bidder's canal and the Bidder's canal is connected to longitudinal collecting tubules by means of a number of transverse collecting tubes and these longitudinal collecting tubules open into the ureter. Finally, they open into the urinogenital duct that emerges from the kidneys. So, the correct answer is option C.

Frog reproduces in water. They are oviparous and they lay eggs in water which is fertilised outside the body of the frog. In order to make sure that the sperm reaches the eggs, the male and female get into a mating posture called amplexus. so, the correct answer is option A.

Vocal sacs are prominent in a male frog. It is composed of flexible skin which easily expands or contracts to change the frequency of sound waves and helps in amplification. The sound produced is a call for mating. The presence or development of the vocal sac is one way of externally determining the sex of a frog in many species. The vocal sac is open to the mouth cavity of the frog, with two slits on either side of the tongue. To call, the frog inflates its lungs and shuts its nose and mouth. So, the correct answer is option A.

In indirect development, an animal's birth form is different from the adult form. The embryo hatches from the egg in the larval form. The larva undergoes a drastic metamorphosis in order to achieve its adult stage. Frog, the adult form is completely different from the tadpole, its birth form. Hence, frog undergoes indirect development.
So, the correct answer is option B.