210 Transactions of the 



into a large glass vessel without lifting the net entirely out of the 

 water, answers very well. 



There appears to be some confusion with regard to the nomen- 

 clature of the position of the body ; Dr. Fol * and also Vogt t 

 term the side on which the nervous system occurs, the dorsal, and 

 the side to which the tail is attached, the ventral. This would be 

 correct in regard to the development of the Ascidia in reference to the 

 vertebrate type of structure. In Professor Huxley's % paper, on the 

 other hand, the nervous system is described as being on the ventral 

 side. In order to avoid this confusion, perhaps it would be better 

 to call the side on which the ganglion is situated the neural, and 

 that to which the tail is attached the haemal ; and in speaking of 

 the direction of any part, whether towards the neural or haemal 

 side, the corresponding terms § would be neurad or haemad. But 

 there still remains the necessity, when referring to the right or left 

 side of the animal, to determine whether the neural side is to be 

 considered ventral or dorsal ; but as in my last paper I followed Pro- 

 fessor Huxley's nomenclature in reference to this aspect, I think it 

 will be preferable still to do so, and in order to distinguish the right 

 from the left side, to speak as if the nervous system were situated 

 on the ventral side of the body. This discussion may appear trivial, 

 but it will be found that the present paper would be unintelligible 

 without some definite rule on the subject. 



It is comparatively easy to obtain a side view of these animals, 

 because, being narrower in that direction than from the neural to 

 the haemal side, they naturally fall into that position when they are 

 slightly confined by the covering glass. But to get a haemal or 

 neural view is much more difiicult ; in this case it is necessary so to 

 arrange the covering glass that it does not touch any part of their 

 body, and being thus free to move about as they please, a good 

 view is a matter of chance and patience. The plan that I have 

 found to answer best, is to support both ends of the cover by a 

 suSicient thickness of paper, to put the animal into a very small 

 drop of water, and by means of a horsehair to draw this drop of 

 water into a point ; when this is done they sometimes drive them- 

 selves into the inlet thus formed, and revolve with great rapidity 

 round their long axis; but after a time they become tired, and 

 remain quiet for a few seconds, when it is possible to gain a view of 

 them in either the haemal or neural position. The specimens that 

 I examined varied in length of body from 0*24 mm. to 0'72 mm. 



Integument. — The whole body, with the exception of the extreme 

 posterior end, is surrounded by a hyaline membrane ; that this is 



* * Mem. de la Societe de Phys. et de I'Histoire Naturelle de Geneve,' torn, xx., 

 12""' par tie. 



t ' Me'm. de I'lnstitut National Genevois,' torn. ii. 

 X ' Quar. Jour. Mic. Science,' vol. iv., 1856. 

 § Derived from Vertebrate Anatomv- 



