CIONA. 



with the vertebrate phylum, and to 

 Kowalevsky must be assigned the first 

 place amongst the many distinguished 

 workers whose labours have built up 

 our knowledge of tunicate morpho- 

 logy. But the Tunicata have other 

 claims to the special attention of 

 zoologists. Most of them possess the 

 power of asexual reproduction by 

 budding. Not only is this noteworthy 

 in a group so near the Vertebrata, 

 but the phenomenon is remarkable for 

 the variable manner in which it is 

 effected. The condition of the coelom 

 appears to be highly peculiar, and the 

 presence outside the ectoderm of a 

 layer containing blood-vessels and 

 nucleated elements is a feature unique 

 in the animal kingdom. 



As a type of the Tunicata we shall 

 take a common example of the simple 

 Ascidians, dona intestinalis. Ciona 

 has an elongated form (Fig. 1). At 

 one end, which we shall call the pos- 

 terior, it is attached by processes of 

 the test to the substratum ; at the 

 other end, which we shall call the 

 anterior, is the mouth- opening, or, as it 

 is often called, the inhalent siphon. A 

 little distance from the mouth on one 

 side of the body is a second opening, 

 the aperture of the atrial cavity or 

 exhalent opening (Fig. 1, 2). The 

 side on which this is placed is called 

 dorsal. The side opposite to that on 

 which the atrial opening is placed is 

 the ventral surface. The whole body 

 is covered by a semi-transparent 

 gelatinous coat, called the tunic or 

 test. The test is a thick, hyaline, 



FIG. 1. Ciona intestinalis, life 

 size (after Shipley and Mac- 

 Bride). Some of the organs 

 can be seen through the semi- 

 transparent test. 1 mouth ; 2 

 atrial aperture; 3 anus; ^geni- 

 tal opening ; 5 muscles of body 

 wall ; 6 stomach ; 7 rectum ; 

 8 ovary ; 9 stolon of attach- 

 ment ; 10 tentacular ring ; 



11 peripharyngeal ring ; 



12 nerve-ganglion. 



