Mr. J. D. Macdonald on a new form of Compound Tunicata. 403 



the branchial opening to the cardiac end of the stomach, where 

 it suddenly curves downwards and outwards to terminate near 

 the inner side of the mouth. A line drawn through the branchial 

 and cloacal openings would be nearly parallel to this latter por- 

 tion of the endostyle, and the transverse bars of the branchial 

 network take the same direction. The more delicate longitudinal 

 nervures, on the other hand, are parallel with the first portion 

 of the endostyle, and rather more closely approximated than is 

 usual in other cases. 



The nervous system mainly consists of two small rounded 

 ganglia (fig. 6 b) lying one upon another, in a right line with, 

 and about midway between, the branchial and cloacal apertures. 

 The deeper one appears to be the larger of the two, and presents 

 a considerable portion of its surface below the other. 



It is rather difficult to trace the course of the nerves which 

 radiate from these centres, both on account of the transparency 

 of the nerves themselves and the manner in which the fibres of 

 the muscular coat intersect them. I have been enabled, how- 

 ever, to follow a delicate tubule from the lateral borders of the 

 larger ganglion to a minute black spot composed of a fine granu- 

 lar pigment, lying at some little distance from the median line 

 on either side ; and in this observation I am supported by Mr. 

 F. M. Rayner, who inspected the original preparations himself. 



Now, the question arises, what is the nature of these spots ? 

 they are not confined to this species, for I have distinctly ob- 

 served their homologues in the zooids of Bigillina. Would it 

 be irrational to surmise that they are rudimentary visual organs ? 

 which indeed their prima facie appearance would naturally sug- 

 gest. Analogy, to a certain extent, forbids this conclusion, and 

 several facts tend to show that they are the remnants of the 

 otolithic sacs (fig. 7 a and fig. 8, more highly magnified) which 

 exist in the larva in close contact with the nervous ganglia*. 

 I must, however, defer any further remarks on this subject to a 

 future period. 



From what has been stated above, it will be seen that the 

 actual relationships of the branchial and cloacal openings, whose 

 position is apparently so anomalous in the present genus, as well 

 as in Boltenia and Cy sting ea, do not difi'er essentially from those 

 which obtain in ordinary Ascidians. 



The endostyle, however distorted, must always indicate the 

 dorsal aspect of the animal ; hence it would be incorrect to con- 

 sider the space included between the branchial opening and 

 pedicle, in the genera alluded to, as part of the ventral surface. 



* The disposition of the otoHthic sacs in relation to the ganglia tends to 

 show that the axis of the future Tunicary is at right angles to that of its 

 embryo. 



26* 



