TUNIC ATE S. 57 



the group, many of which are found on our shores. Some of the most common forms 

 belong to the genus Molgida, and individuals of the various sjoecies are found at- 

 tached to rockB 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 very pretty appearance. Possibly most com- 

 mon of all is Molgula manhattensis, which I have 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 becomitig attached fig. w.—Mnhmia 

 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 frequently 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 Eugyra embraces a number of small spherical species, 



fond of muddy bottoms, where they live imattached. The embryology 



of a species of this genus has been studied by Lacaze Duthiers (he calls 



it Molgula), and he finds that it does not have a tadpole larva. The 



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



appropriate name ' sea peach ; ' for they are large and neai-ly spherical, 



^"^^piiiuiaris''''"' ^''^'^^ ^^^ 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 animals will contract still further if touched, sending 



streams of water out of both oral and atrial apertures. 



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

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

 in color, and ai*e 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 ^\•ith numbers of seaweeds, hydroids, 

 and other forms of animal and vegetable life. 



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

 is much like the members of the last family, the distinguishing featm-e 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 copnected by a common stem. In these buds both 

 entoderm and ectoderm are concerned. The latter is derived, of course, fi-om the 

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

 sac. The principal genera are Clavellina and Perophora. 



Oedee III.— SYNASCIDIiE. 



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

 Compositee. In all the species numerous individuals are enveloped in a common 



