CEARAGTEltlSTlCS OF TUJ^IGATES. 405 



in size, loses its gills and alimentary canal, while its muscu- 

 lar system becomes powerfully developed. The median buds 

 develop into individuals, which resemble the sexual animals, 

 except that they are without genital organs; they, therefore, 

 represent a second generationof asexual forms, whicli become 

 free and produce the sexual generation from a ventral sto- 

 lon."* 



Class I.— TUNICATA. 



Body visually mhspherical, or sae-like, obscurely symmetrical ; some, 

 times barrel shape.d, bilateral, with a dorsal and ventral symmetry, pro- 

 tected by a transparent or dense test, ci/ntainiiig cellulose, lined withiii 

 by a tunic surrounding the body-cavity. Two openings in the test, one 

 oral, the other atrial ; moutli leading into a capncious pharyngeal ris- 

 pirntory sac, opening posteriorly by an asophagus into a stomach, which 

 ii prodded with a liver; intestine flexed, vent opening near the cesophagus, 

 the fcEces parsing into an atrium or cloacal space, and thence out of the 

 atrial opening. Nervous system bilateral, forming a double ganglio- 

 nated chaia {Appendicularia), but usually reduced to a single ganglion, 

 M'.uated within the tunic between the tw) openings ; a tubular hea.rl, open- 

 ing at each end, lodged in- a sinus-system, ani its beatings often reversed, 

 the blood flowing in and out at either end. S -xes usually united ; in some 

 forms asexual individuals ; reproducing by eggs or budding partheno- 

 geneticaXly, or by gemmation. 



Order 1. Ascidiac.ea. — Body sac-like, subaplierical, usually sessile, 

 sometimes stalked, simple pr compound, minute individuals 

 growing in a common mass ; tlie oral and atriiil openings 

 contiguous ; often a com])lete metamorpliosis. (Appendicu- 

 laria, Botrylius, Amaroecium, Clavellina, Peropliora, As- 

 cidia, Boltenia, Pyrosoma). 



Order 3. Thaliacea. — Body barrel-shaped ; free-swimming, test thick, 

 hyaline; with circular muscular bands; respiratory sac 

 widely open ; reproducing by alternation of generations. 

 (Salpa, Doliolum). 



Laboratory Work. — The Tunicates can well be studied only in a 

 living state; or sections of hardened Salpse may be made. The young, 

 caught with the tow-net, should be immediately examined, as they 

 are very short-lived. Delicate sections of hardened eggs and larvse 

 are made with great difficulty, but are necessary to examine in con- 

 nection with the living, more or less transparent animals. 



* Claus, Zoology, English edition, ii. p. 107. 



