CHARACTERISTICS OF TUNICATES. 4o5 



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 generation of asexual forms, which become 

 free and produce the .sexual generation from a ventral sto- 

 lon."* 



CLASS I. TUNICATA. 



Body usually subspherical, or sac-like, obscurely symmetrical ; some- 

 time.? barrel shaped, trilateral, with a dorsal and ventral symmetry, pro- 

 tected by a transparent or dense test, continuing cellulose, lined wit/tin 

 by a tunic surrounding the body-cueity. Tiro openings in the test, one 

 oral, the, other at rial; mouth leud'tnt/ into a capacious phuryngeal r<s- 

 pirntory sac, opening posteriorly by an. <vwph<i'jii8 into a stomach, which 

 is prodded with a liver; intestine flexed, rent opening near the (Ksopliagus, 

 the faces passing into an atrium or cloaca? *ni<", and thence out of the 

 atrial opening. Nervous system bilateral, forming a double gangli'>- 

 nated chain (Appendicularia), but usually reduced to a, single yan</li<in, 

 situated within the tunic between the t/c-i openings ; a tubular heart, op 'n- 

 ing at each end, lodged in. a sinus-system, an I its beatings often n-r< rsed, 

 the blood flawing in and out at either end. S xes usually un ited ; in some 

 forms asexual individuals ; reproducing by eggs or budding parlheno- 

 _genetically, or by gemmation. 



Order 1. Ascidiacea. Body sac-like, subspherical, usually sessile, 

 sometimes stalked, simple or compound, minute individuals 

 growing in a common mass ; the oral and atri;d openings 

 contiguous; often a complete metamorphosis. (Appendicu- 

 laria, Botryllus. Amarcecium, Clavellina, Peropliora, As- 

 cidia, Boltenia, Pyrosoma). 



Order 2. Thaliacea. Body barrel-shaped ; free-swimming, test tliick, 

 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 Salprc 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 larvae 

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

 nection with the living, more or less transparent animals. 



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



