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and temporarily with an organ that, in its position, had the 

 greatest resemblance to the corda dorsalis, or spinal-chord of 

 the vertebrate animals (fishes, reptiles, birds, mammals, and such 

 like). This organ is an elastic cartilaginous string, along which, 

 in the animal in question, is laid the spine and its marrow, 

 and which, in the lowest form of the vertebrates, the lancet fish, 

 Amphioxus) remains for life, but is lost in the larvae of the 

 Ascidians during the retrograde transformation by which the 

 unattached larva becomes a fixed ascidian. The conclusion 

 drawn from these facts is in harmony with the scientific theory 

 according to which every individual, during development, passes 

 through a series of forms inherited from its ancestors during 

 the course of the earth's history. Just (to choose a more fa- 

 miliar example), as it is deduced from the fish-like shape and 

 organisation of the tadpole , that fishes were the ancestors of 

 amphibians, or, which is the same thing, that frogs originate in 

 fish-like vertebrates ; so, from the temporary appearance of the 

 spinal chord in the larvae of the Ascidians, it is deduced that 

 these animals are connected with the vertebrates by a common 

 original form. This theory, however, cannot yet be regarded 

 as a scientific fact, the difficulty of examination being so great; 

 and lately another theory has been opposed to it, according to 

 which the ancestors of the vertebrates are rather to be looked for 

 in animals like the higher worms or annelids in the Aquarium. 

 All the Ascidians are hermaphrodites, that is animals which 

 unite both sexes in one individual. Besides sexual generation 

 which produces unattached swimming larvae from impregnated 

 eggs, there exists in this group an unsexual generation by bud- 

 ding, to which the colonies owe their origin. 



Opposed to the Ascidians as adhesive or attached animals, are 

 the Salpae as swimming animals. Their delicate transparency 

 shows them at once to be pelagic animals, which, like jelly- 

 fish, live in the open sea, and are carried, together with the 

 other representatives of the pelagic world, by winds and cur- 

 rents to the coasts, where they are often caught by thousands 

 in the fishermen's nets, -a very unwelcome catch indeed. 



All the year round, but especially in Spring and Autumn, 

 salpae are brought to the Aquarium, where, like other pelagic 

 animals, they are exposed in separate glass vessels.. It will not 

 be difficult for the spectator, guided by the following remarks, 

 to make himself acquainted with the general construction of a 



