362 REPORT — 1892. 



be induced by an artificial tide of different duration to the natural 

 one. 



On tbe other hand, the results of the investigation are not altogether 

 satisfactory, on account of, first, the large number of specimens that 

 became unhealthy during the pi'ogress of the experiment; second, the 

 fact that the only three specimens that survived in the tank with the 

 artificial tide were taken from the deep water off the Eddystone. 



Far more satisfactory results would probably be obtained, if experi- 

 ments were tried upon a number of Alcyoniums taken from shallow 

 water direct and placed in the tanks. Many of the specimens collected 

 from the Catwater were probably taken by the trawlers from deep water 

 and thrown overboard as they entered the hai'bour, and were in conse- 

 quence in an unhealthy condition when collected. 



The subject, however, seems to me to be worthy of further investiga- 

 tion. 



III. Report on the Occupation of the Table. By Mr. Arthur Willet. 



I spent six weeks in the laboratory at Plymouth during the months- 

 of August and September 1891. 



I was at first engaged in the study of a new genus of compound 

 ascidians from Japan, belonging to the family of the Didemnidte, and 

 have already published a short description of it, in conjunction with my 

 friend Mr. Asajiro Oka, in the ' Quarterly Journal of Microscopical 

 Science ' for January 1892. 



I also made observations on the tadpoles of Styela grossularia, and of 

 another small red and white Ascidian which lives on shells and .stones at 

 the bottom of the Sound, and occurs in mulberry-like masses, and which 

 I take to be Polycarpa glomerata. In these forms the embryonic 

 development up to the stage of the free-swimming tadpole takes place in 

 the peribranchial chamber, a portion of which is converted into a special 

 brood pouch traversed by vascular trabeculae. The tadpoles of these 

 Ascidians are remarkable for possessing a complete ring of hollow ecto- 

 dermic tentacle-like processes which surrounds the anterior portion of 

 the larva, at the extremity of which are borne the three adhering papillee. 

 The mouth is not enclosed by this ring of tentacles, but lies outside it. 

 Similar tentacles occur in the tadpoles of the Botryllidse and the Didem- 

 nidse. 



Their presence in Simple Ascidians is rather extraordinary, and seems 

 to occur in correlation with the fact, already mentioned, that in these par- 

 ticular Simple Ascidians, by way of an exception, the development up to 

 the tadpole stage takes place in the body of the parent. The large 

 quantity of yolk which renders the eggs and larvae of these forms so 

 opaque must also be brought into relation with the mode of development. 

 It seems to be a general rule that in the Simple Ascidians the embryonic 

 development is a pelagic one, while in the Compound Ascidians the 

 development takes place in some part or other of the parent colony. To 

 this rule, of course, the two species of Simple Ascidians mentioned above 

 form exceptions. 



In the living tadpole blood can be seen flowing into the tentacles. 

 They are capable of distension and contraction according to the degree 

 of turgidity in which they are kept by the blood inside them. Their 

 actual function is at present that of accessory adhering organs. When 



