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Updated: May 15, 2025
Sexually mature specimens of the Amphioxus, which are found in great quantities at Messina from April or May onwards, begin as a rule to eject their sexual products in the evening; if you catch them about the middle of a warm night and put them in a glass vessel with seawater, they immediately eject through the mouth their accumulated sexual products, in consequence of the disturbance.
We may, however, trace man's genealogical tree not only as far as the lower mammals, but much further to the amphibia, to the shark-like primitive fishes, and, in fine, to the skull-less vertebrates that closely resembled the Amphioxus.
In order now to infer from these and similar facts that man at one time really existed in this scarcely vertebrate condition of the amphioxus,—a conclusion which, strictly understood, yields no meaning,—we can make the case much more easily conceivable if we represent the thinking, or invention of the world, as an ascending scale, in which even the least chromatic tone must have a place without a break, while the principal tones do not become clear and full until the requisite number of vibrations is attained.
Though the Amphioxus has many peculiarities of structure and has much degenerated, and though it cannot be regarded as an unchanged descendant of the Primitive Vertebrate, it must have inherited from it the specific characters we enumerated above.
All these, moreover, pass, during their embryonic development, through a stage in which their whole organisation is no higher than that of the Amphioxus, but is substantially identical with it. In order to see this quite clearly, it is particularly useful to compare the Amphioxus with the youthful forms of those vertebrates that are classified next to it. This is the class of the Cyclostoma.
The fossil referred to is an ancient fish-like worm, or worm-like fish, to which the name of Entomicthys amphisoma has been provisionally given. It is still more remarkable than the amphioxus or lancelet, which has been long known.
All the other vertebrates have a compressed, thick, pouch-shaped heart, which develops from the wall of the gut at the throat, and from which the blood-vessels proceed; in the Amphioxus there is no special centralised heart, driving the blood by its pulsations.
This makes all the more interesting the striking resemblance of its immature larva to the developed and sexually mature Amphioxus.
Here we find such an enormous variety of vertebrate souls that, at first sight, it seems quite impossible to trace them all to a common "Primitive Vertebrate." Think of the tiny Amphioxus, with no real brain but a simple medullary tube, and its whole psychic life at the very lowest stage among the Vertebrates. The following group of the Cyclostomes are still very limited, though they have a brain.
We call this layer the blastoderm, and the sphere itself the blastula, or embryonic vesicle. This interesting blastula is very important. The conversion of the morula into a hollow ball proceeds on the same lines originally in the most diverse stems as, for instance, in many of the zoophytes and worms, the ascidia, many of the echinoderms and molluscs, and in the amphioxus.
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