718 REPORT — 1895. 



Enough of the facts are now before us to enahle us to state the problem clearly. 

 If the property of budding has been independently acquired by two quite widely 

 separated groups of simple ascidians, how has it come about that the development 

 of the blastozooids agrees so closely, and in such remarkable jjeculiarities, as the 

 orioin of the nervous system, and the peribranchial sac from the outer layer of the 

 evxbryo and from the inner layer of the hud ? 



I believe the answer to be that we have before us an excellent case of develop- 

 mental opportunism. The inner layer of the bud gives origin to nearly all the 

 ort^ans of the blastozooid because physiological influences working to such a course 

 of development have been stronger than the hereditary influences tending to make 

 the development follow the embryonic method. 



The case is particularly interesting because, as I believe, we are able to put our 

 fino-er on the physiological cause that has been so potent in modifying the directmi, 

 not thejinal result of the mighty force of heredity. 



You will remember that the outer layer of the embryo produces the matrix of 

 the test, the nervous system, and the peribranchial sacs. Kow observe. The pro- 

 duction of the two last-mentioned structures is a jmrely developmental matter. It 

 concerns the embryonic period only. The organs become separated, or practically 

 so, from their source during this period, and the outer layer has nothing more to 

 ' do with them, at least functionally. Not so with the production of the test. This 

 is not merely an embryonic matter ; it is an enduring physiological matter. 

 The test must be constantly renewed throughout the life of the individual. The 

 outer laver is consequently an active secretory organ from an early embryonal 

 period to the end of the animal's life ; and since the outer layer of the bud is 

 merely a portion of the outer layer of the parent or of the stolon, as the case may 

 be, it is at no time an einhryonic layer ; it is, from the very beginning, a differ- 

 entiated organ. It has to grow, to be sure ; but in addition it has a well- 

 established and important physiological function to perform. Very difl^erent is it 

 with the inner layer. Its cells are strictly undifferentiated — embryonic, if you 

 will. They do not even have to digest their own food, for they are constantly 

 bathed in the maternal blood. The layer does not come in contact with the 

 external world at any time or at any point. It has nothing to do but to develop. 

 Why should it not relieve the outer layer from producing some of the parts that 

 it produces in the embryo ? And it does. 



I must hasten to say that this physiological explanation of the peculiarities of 

 ascidian bud development was suggested by Seeliger, though he did not make as 

 much of it as I believe it deserves. 



There are several other instances among budding animals where I am inclined 

 to think that assignable functional influences have more or less radically changed 

 the method of development, but time prevents reference to more than one of 

 these. Chun has very recently shown that in liathkea octojmnctata , one of the 

 Medusae, the inner layer of the parent takes no part whatever in the formation of 

 the bud. The buds are produced on the wall of the stomach, and it appears to 

 me highly probable that the ectoderm alone shares in the process, because the 

 endoderm is so completely^ given over to the digestive function, while the ectoderm 

 cells have much more largely retained their undifferentiated condition owing to 

 their being in great measure protected from the external world by the sub- 

 umbrella. 



11. Outlines of a neto Classification of the Ttmicata. 

 By Walter Garstang, 3f.A., F.Z.S., Fellow of Lincoln College, Oxford. 



Professor Herdman's classification of the Tunicata is based very largely upon 

 modifications of external form connected with gemmation and the formation of 

 colonies. It involves, as Professor Herdman himself admits, an unnatural separa- 

 tion of forms admittedly allied, e.g., Fyrosoma and Doliolum, Claielina and the 

 Distomidse, Diazona and Ciona, as well as to an rmnatural approximation of forms 

 whose structure is altogether dissimilar, e.g., Fyrosoma and Ccclocorinus, Terophora 

 and Claoelina. 



