Pl. I · Testis

The plate

The specimen, drawn

Pl. I

The headRounded proximal end that fits into the acetabulum of the hip bone. as it was cut, with the seminiferous tubule wall laid out flat below it and the gradient read at ×400 in the circle.

Habitat & range

Where it lives

Body map

Paired, in the scrotum, outside the body cavity — which is the whole point of where they are.

Range

• Scrotal, outside the abdomen, and a few degrees below core temperature — spermatogenesis will not run at 37 °C.
• About 4–5 cm long, in a tough capsule, the tunica albugineaA fibrous layer surrounding the ovary., divided into roughly 250 lobules.
• Each lobule holds one to four seminiferous tubules; uncoiled, the tubules of one testis run to about 250 metres.
• Roughly 100 million sperm a day, and every one of them starts against the basement membrane.

Collection record

• Add your slide numbers here.

Niche

What it does for a living

Make four haploid cellsThe basic structural and functional units of life. out of one diploidA cell with two sets of chromosomes, one from each parent (2n). one, several hundred million times a day, in a compartment the immune system is not allowed into — and keep the whole production line cool enough to work.

field collected specimen

How to know it on sight

• Round tubule profiles packed close together, each with a wall several cells deepAway from the surface of the body. and a pale open lumenThe inside space of a hollow organ or structure. in the middle.
• The wall is a gradient, not a jumble: big dark nucleiClusters of neurons in the CNS responsible for processing information. on the basement membrane, smaller paler ones as you move inward.
• Tails. At the luminal edge, fine dark comma-shaped nuclei with threads trailing off them.
• Between the tubules, in the stroma, small clusters of large pale cells — Leydig, and the only endocrine cells here.

Specimen 1

Tubules in H&E. Dark purple spermatogenic nuclei packed around a pale lumen, with reddish-pink connective tissue between.

Specimen 2

Several tubules at once. Read the wall of each one from the outside in and you have read the whole process.

Specimen 3

Low power: testis above, epididymis below. Tubules with germ cells in the wall, against ducts with cargo in the lumen.

People keep calling her by the wrong name

Look-alikes

Two plates. The first is the other gonad, which keeps its stages in whole folliclesStructures in the ovaries that contain developing oocytes. rather than cell rows; the second is the duct next door, where the sperm are passengers and not residents. A third trap — the thyroid — is round profiles with contents too, but the contents are colloidA mixture where small particles are dispersed but not dissolved in a liquid. and the wall is one cell thick.

Ovary

The other gonad. Also a stage gradient, but the stages are entire follicles of increasing size, and there is one oocyte in each.

Epididymis

A duct. One row of cells with nuclei at several heights, a fringe of stereocilia, and sperm lying loose in the middle.

Examine it yourself

The virtual slide

Start low and find the round profiles. Then pick one tubule and climb its wall from the basement membrane to the lumen, naming each row as you go. Last, look outside the tubules for the Leydig cells.

Virtual slide courtesy of Histology Guide.

Field notes

Why this organism

A sunflower head is not one flower, it is roughly 1,500, and they open in a spiral from the outside in. Photograph one and you have a map of time: the rim is finished, the middle has not started. Cut a seminiferous tubule across and you get the same photograph, except the axisSecond cervical vertebra; has the odontoid process (dens) for pivoting head (“no” motion). runs from the basement membrane to the lumen instead of from rim to centre. Both are production lines that solved the problem of showing every stage at once by putting the stages in space instead of in sequence.