TUNI(\ITKS. 



57 



the grou]), many of whk'li arc l'<iun(l on our sliort's. Sonic of the most common forms 

 belong to the genus Molyida, and individuals of the various species are found at- 

 tached to rocks and piles, from half-tide mark down to a depth of several fathoms. 

 They are rather small, a large one reaching a diameter of about half an inch, and are 

 usually a pellucid yellow, allowing the color of the viscera to be indistinctly seen, 

 giving the whole animal a vei'v ])retty ap])earancc. Possibly most com- 

 mon of all is Mulytda manhattensis, which I liave found in favorable 

 places in countless myriads. In this species the young undergo a por- 

 tion of their development in the cloaca, and when the tadpoles hatch 

 they swim out as yellow atoms. They form adhesive processes like 

 those described above, but they cannot use them in becomintr attache<l Pic. n.—MnUiuta 



. "^ . . " mduhntUii^i!, 



to rocks and stones, since they are entirely enclosed in a peculiar en- 

 velope. This envelope, however, is after a while very adhesive, and if the little tadpole 

 happens to touch any part of himself to a stone or shell he is fastened for life. Thus I 

 have fre(juently seen them adhere by the tail, while the anterior part was making the 

 most violent struggles to escape. Soon, however, they settle down contentedly, absorb 

 the tail, and in a few weeks assume the adult structure. These young possess consid- 

 erable vitality, as I have kept them for several weeks without changing the water. 



The genus Euffyra embraces a numl)er of small spherical species, 



fond of muddy bottoms, where they live unattached. Tiie embryology 



of a species of this genus has been studied by Lacaze Duthiei's (he calls 



it ^rolijula), and he finds that it does not have a tadi)ole larva. The 



fishermen call some of the species of the genus Cynthia by the rather 



appropriate name 'sea peach;' for they are large and nearly s])herical, 



^^^'^UMarii!''"' while the colors, red and yellow, are disposed much as in the familiar 



fruit. The name 'sea squirt' is also given, from the fact that when 



drawn to the surface these aniirials will contract still further if touched, sending 



streams of water out of botli oral and atrial apertures. 



The only other genus which we shall mention is Boltenia, which embraces the 

 ' sea pears ' of the fishermen's terminology. These species are usually j'ellow or reddish 

 in color, and are supported on long and slender stalks which sometimes attain a 

 length of a foot or more. The body proper is pear-shaped, with the openings on one 

 side. The tunic is tough, wrinkled, and leathery, and the animals are utterly unable 

 to keep themselves clean, but are always covered with numbei's of seaweeds, hydroids, 

 and other forms of animal and vegetable life. 



The family Clavellixidye embraces the social ascidians. In structure each of these 

 is much like the members of the last family, the distinguishing feature being that the 

 first individual formed sends out a bud which grows into a root-like stem, developing 

 another individual at the extremity. This second one repeats the operation, and the 

 result is a rather large colony connected by a common stem. In these buds both 

 entoderm and ectoderm are concerned. The latter is derived, of course, from the 

 outer layer of the body, but the entoderm arises as an outgrowth from the branchial 

 sac. The principal genera are Clavellina and Perophora. 



OiiDEi: III. — SYNASCIDI^. 



This is one of the groups of compound ascidians, and is frequently termed Ascidiffi 

 Composit£E. In all the species numerous individuals are enveloped in a common 



