this is making the "it just looks like sperm" theory look more and more likely

Hmmm, I'm going to have to work harder on this, aren't I?

Straight up, FB, people did believe that sperm was produced in the brain, piped down the spinal cord, on into the testes, which were seen more as mini bladders. Remember that knowledge of anatomy was quite limited right up until the 19th C (when people like Burke & Hare provided plenty of dissection material ), and even then, if you've ever done a dissection, you'll know that real creatures (and even plants) don't look anything like those clear-cut diagrams from which we learn. Things rapidly turn into an amorphous gooey mess.

All you need to add to this situation is a physiological paradigm that placed a very strong faith in the ancients, and perhaps the fact that human cerebro-spinal fluid has a vague similarity to semen. Oh, and sperm whales having such huge brains probably played a part.

An excerpt from The Household Cyclopedia of General Information (1881) makes it clear that spermaceti was genuinely seen as whale sperm:
http://makeashorterlink.com/?W11C26371

This is a brilliant example of how history gets rewritten after a new paradigm has been adopted, making it look like that paradigm is a logical continuation of all that went before. The truth is the new medical/physiological paradigm turned the old "scientific" beliefs completely upside-down.