A MOLLUSCAN TADPOLE. 279 



in circular groups. The orifice of each tube has four delicate 

 processes radiating inwards, like the spokes of a wheel, or 

 like the processes in the siphon of a cockle. This orifice is 

 alternately protruded and retracted, but does not open and 

 shut like that of an Ascidian ; and, moreover, the orifice is 

 single. The heart, or pulsating sac, lies at the bottom of the 

 visceral cavity. Imbedded in the clear gelatinous base are 

 several branching vessels giving off pear-shaped processes. 

 These vessels'connect the visceral cavities of the whole colony, 

 and the globules of food are seen oscillating to and from the 

 cavities into the pear-shaped processes. I was completely 

 puzzled what to consider this animal, until I saw a tadpole 

 embryo escape from it, and swim away, followed by several 

 others ; and then I knew an Ascidian of some kind was 

 before me. 



A tadpole ? Well, that is a figure of speech. The embryo 

 of the Ascidian is more like a tadpole than anything else ; 

 and totally unlike its parent, not only in possessing a good 

 long tail, but in being able to swim vigorously through the 

 water in which the parent is immovable. In the interior of 

 the round body which surmounts this tail, a mass of yellowish 

 granules (the vitellus) is observed, which extends some way 

 down the axis of the tail. The transparent membrane sur- 

 rounding the granular mass enlarges. The mass develops 

 three processes, which act as suckers, wherewith the animal 

 finally fixes itself for life. The tail then becomes absorbed, 

 as in the tadpole.* The viscera appear; the envelope 



* Some writers describe this disappearance of the tail as a fission, the tail 

 dropping off. I have not observed this. The enveloping membrane, as it 



