106 JOURNAL OF MARINE ZOOLOGY AND MICROSCOPY. 



longitudinally along the dorsal side of the body. The edges gradually 

 grow upwards and inwards to meet, and thus form a tube which now 

 constitutes the central nervous system of the animal. 



The anterior end gradually swells into a large vesicle, while from 

 the hinder end of this, there runs a rapidly narrowing tube which is 

 prolonged into the tail as the caudal nerve. The large anterior 

 vesicle contains two peculiar sense organs, an eye, and an otolith 

 perhaps of auditory value. These can readily be made out in 

 mounted specimens, as both are darkly pigmented and show 

 conspicuously, rendering easy the location of the cerebral vesicle 

 lying between the mouth and the atrial opening. Of the two, the 

 eye is much the more complex, for it possesses a cup-shaped retina 

 in which is placed a projecting and complex lens. It is placed at 

 the posterior upper corner of the vesicle and projects downwards 

 towards the centre of the cavity. The otolith on the other hand, 

 rises upon a stalk from the floor of the vesicle more to the front end. 

 It is noteworthy that both are within the vesicle. 



The after history of the animal is quickly told. The larva 

 affixes itself by the glutinous secretion of one or all of its three 

 papillae to some object ; the tail with its contained notochord, as well 

 as the three anchoring papillae become absorbed ; the test becomes 

 enormously thickened and strengthened, and the perforations of the 

 pharynx become multiplied greatly, and most significant of all, eye 

 and otolith vanish utterly, the well developed nervous system being 

 reduced to a fairly large ganglionic mass occupying the position of the 

 cerebral vesicle of the larva, i.e. midway between the mouth and the 

 atrial opening. Radiating nerves to the various organs are thence 

 given off. The course of these changes brings about a certain alter- 

 ation of placing of the two external apertures, as may be seen in the 

 diagrams ; thus the mouth in the fixed larva of Apiidiam is at first 

 not terminal, but gradually becomes so, thus necessitating a corres- 

 ponding travel of the atrial opening. There is, however, no real 

 travel of these parts, simply a more rapid growth than of the opposite 

 side, of that part of the body wall and test lying below the mouth, 

 i.e. between it and the point of attachment to the rock. This 

 naturally pushes the mouth upwards, and finally places it in a 

 terminal position, at the point of the body furthest removed from 

 the point of fixation. Budding produces a cake-shaped colonial mass 

 of a general pink colour, flecked with white points indicating the 

 position of the mouths of the various individuals or ascidiozooids. 



With the assumption of adult form by Simple Ascidians, the 

 genital glands develop, but among the Compound, a frequently long- 

 continued course of budding, takes place prior thereto. All species 

 are hermaphrodite, but as a rule the male and female organs do 



