Of planaria and . . . Elephants?

I love the world wide web. For better or worse, today it is easier than ever to obtain information. This is especially important for science, because in science, information is the name of the game. When I was an undergraduate (I almost said, “In my time…“), if you wanted to get the latest papers in your field you had to actually go to the library and look over the available printed journals or check out the newest issue of “Current Contents” (look it up!). Nowadays, when a paper appears, it is usually available online (free or for a price; this is a story for another day) for your reading pleasure. This is possible because of all the new technological advances which, whether we like it or not, are here to stay.

As much as I like new technologies (all scientists do) sometimes I feel that “The New” is overrated. There is a sad tendency to equal “newness” (is this a word?) with higher relevance and even value. An unfortunate consequence of this state of mind is to think that somehow, an old book is useless. Nothing is further from the truth. Whenever I can, I like reading old books (100+ years old) about natural history. More than once I find many interesting gems that give me a glimpse of the author’s thought process and even learn things that I had never even heard of. Also, reading older books is one of the best antidotes against believing that one was the first one to think about something.
Priority is an important concept in scientific research, but a real scientist always make an honest effort to at least try to find out if she/he is truly “the first”.

If you are one of my readers, you probably know that I do research on planarians. Recently I found an electronic version of the book “Observations of some interesting phenomena in animal physiology, exhibited by several species of planariae” by John Graham Dalyell, published in 1814. This very readable book is one of the classic works on planarians and it is widely considered to contain one of the earliest scientific descriptions of planarian regeneration, including a description of two-headed planarians no less!

On page six of the preface he writes:

Possibly, analogous enquiries have long ago been instituted by those more qualified for the task; and, what has appeared obscure in the nature of the animals now brought under consideration, may already be elsewhere satisfactorily explained.

You just have to admire the humbleness of a true scientist; that’s the way to do it! In modern times, the usual phrasing is:

To the best of our knowledge, this is the first observation…

But the spirit is the same.

Planarians are carnivores; further, they can also be hunters. For example, they prey on Daphnia, small crustaceans sometimes known as “water fleas”. When planarians sense Daphnia, they secrete a sticky fluid which immobilizes the water flea and then the worm wraps itself around it just like a constrictor snake (I think a have a picture of this in the lab; if I find it, I will update this post). Once in position, the worm extends its proboscis (also known as pharynx), a tube-like organ that contains its mouth, which doubles up as its anus (try not to talk about this in a first date…). The pharynx excretes digestive substances that partially liquify the insides of the prey and facilitates eating.

Better than Science Fiction, right?

Anyway, based on his observations, the planarian pharynx reminded Dalyell of an elephant’s trunk. In fact, taxonomically, elephants belong to the order Proboscidea, which literally means “the part that eats is located at the front”. Modern elephants are the only extant (living) examples of this order. Other examples include mammoths, mastodonts, etc.

Dalyell writes,

In imitation of the name bestowed on the trunk of the elephant, the extensile organ serving to imbibe the nutriment of many of the smaller animals (Baldscientist’s note: he is referring to the planarians), is called a proboscis…

I believe that this is the first time when the planarian pharynx was referred to as a proboscis. These connections are interesting. By reading Dalyell’s book, I learned the origin of one of the terms that us planarian researchers (or is it researchers using planarians?) use on a daily basis.

I like old books.



7 thoughts on “Of planaria and . . . Elephants?

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