Jet

Huo Gu awkwardly realized that the driving force generated by the flagella serving as "oars" did not seem sufficient to propel a cell cluster whose number of cells had drastically increased.

"Looks like I need to redesign a few things."

As it focused its thoughts, a three-dimensional structural diagram of the cell cluster appeared in Huo Gu's mind.

So how should it improve it?

"Uh... the main issue is still the driving force. Maybe I should start there."

"The driving force is insufficient mainly because the flagella are too short. This means the water they push generates too little forward force to drive the entire cell cluster at high speed."

"So... for the current cell cluster, the flagella can only serve as small engines for adjusting direction. They can no longer be the primary source of power."

The problem now was what kind of main engine Huo Gu should install for the cell cluster.

An image of the spinal tail used by torpedoes appeared in Huo Gu's mind. Combined with muscles, it could sway the water and provide forward thrust.

However, Huo Gu dismissed the idea again.

A fish-like spinal tail required a spinal skeleton to function. Redesigning an entire skeletal system involved far too many considerations, such as water pressure, skeletal weight, and so on.

And Huo Gu needed to leave this dangerous volcanic area as soon as possible.

"I won't think too much about spinal tails for now..."

Images of propulsion systems used by marine creatures throughout Earth's history flashed rapidly through Huo Gu's mind.

Arthropods were out. Their mobility mainly relied on crawling. Their only advantage was their ability to function both in water and on land; otherwise, their limitations were too great.

Suddenly, inspiration struck Huo Gu's wandering thoughts.

"Right, I can try the jet propulsion method used by mollusks."

Jet propulsion, as the name implied, involved drawing water in and then expelling it.

During this process, muscle tissue compressed the water and gave it sufficient kinetic energy. According to Newton's third law—"The forces of action and reaction between two objects are always equal in magnitude, opposite in direction, and act along the same straight line"—the reaction force from the expelled water could achieve movement through water.

The advantages and disadvantages of this method were both obvious. Its advantage was that it could reach a very high speed in a short time underwater. Its disadvantage was that it easily ran out of momentum and lacked the more sustained propulsion of a spinal tail.

After all, once the water used as propulsion medium was exhausted, it would need to stop and replenish its supply.

Without further delay, Huo Gu immediately began improving the cell cluster.

The jet propulsion method could be divided into three stages: the intake stage, the accumulation stage, and the ejection stage.

As long as these three stages could be completed in one cycle, the jet propulsion engine would be complete.

First, it needed to design a cavity capable of holding liquid.

This cavity could not be too small, because it held the propulsion medium and was directly related to how long the cell cluster's propulsion could last.

This was no difficult task for Huo Gu, which could command the cells. Before long, a new cavity formed at the tail end of the cylindrical organism.

Next came the design of the water intake. Huo Gu placed these openings at the front, so that the inertia of forward movement could effortlessly guide water into the cavity.

For the intake, Huo Gu used multiple intake valves, controlling their opening and closing through the mitochondria inside the cells.

This was to ensure that, during the accumulation stage, water would not flow backward out through the intakes.

"Next is the accumulation stage..."

As it spoke, Huo Gu concentrated its attention on individual cells. It needed to create a muscle cell template.

The greatest difference between muscle cells and other cells was that they contracted, and contracted quickly. In addition, their resistance to fatigue was outstanding among cells.

However, Huo Gu did not intend to modify cells according to the muscle cells in its memories.

The intricacy and complexity of those muscle cells far exceeded the effort required to construct an entire skeletal system.

In fact, when Huo Gu had first encountered muscle cells, it could not help but wonder whether living organisms were truly natural products. If no external force had intervened, how could such exquisite and complex microscopic structures exist?

The precise structure of muscle cells existed so they could correctly receive electrical signals from the brain, contract at any moment, and move the body.

But Huo Gu could bypass that point. It could directly command the cells.

"Now that I think about it, I have my own advantages too. Maybe I can try combining them with mitochondria..."

The new type of cell it needed to create would have a simple structure and be capable of imitating the contractions of muscle cells...

So how could it imitate muscle cells to achieve contraction?

At present, Huo Gu possessed two types of mitochondria. One processed sulfur, while the other processed hydrochloric acid to produce hypochlorous acid.

"I'll retain the shape of muscle cells and divide them into multiple sections. The oxygen expelled from the cells will combine with hydrogen to form water. Muscle cells that lose a large amount of oxygen will inevitably contract. That way..."

The biological jet engine gradually became more refined within Huo Gu's sea of thoughts, continuously spewing forth as it operated.

Then came the ejection stage. To achieve ejection and sustain it, the ejection valve needed to be small, but not too small. Otherwise, its output would be insufficient. It also needed a certain degree of elasticity.

Huo Gu continued to use muscle cells. This made the output power of the ejection valve controllable as well.

"I almost forgot. There's also the rudder."

While moving at high speed, encountering obstacles was unavoidable. It therefore had to be able to turn flexibly.

Thus, two pairs of "little fans" appeared on either side of the three-dimensional cell cluster model in Huo Gu's mind. Using fish terminology, these little fans were called "fins."

By using muscle cells to properly adjust the angles of the fins, it could rapidly ascend, descend, and turn underwater within a short period of time.

When the final cell settled into place, the fully designed cell cluster activated this newly formed underwater engine. As it imparted kinetic energy to the water inside the cavity, the long cylindrical tail visibly curved into an arc. From afar, it looked like a carefully crafted porcelain vase.

Boom!

Accompanied by a burst of sound waves traveling through water and a cloud of stirred-up volcanic ash, Huo Gu's cell cluster vanished from its original position.

"Holy shit!"

The underwater engine had worked far too well. The speed the cell cluster had reached completely exceeded Huo Gu's expectations.

Desperately dodging the jagged volcanic rocks on the seabed, it felt as though it were riding a rocket through an interstellar asteroid belt.

Each time, it barely avoided the rocks. Crashing into one of those volcanic formations was only a matter of time.

Fortunately, this was not land. Huo Gu had another option.

"Ascend! Ascend!"

Guided by the flow of water around the fins, the cell cluster made an emergency turn and climbed almost vertically upward.

Behind it, another burst of eruptive flow swept out, as though offering a final farewell.