202 



SCIENCE. 



[N. S. Vol. VII. No. 163. 



of aluminoid ammonia is practically worth- 

 less on account of the organic debris. 



The main difficulty in the various methods 

 seems to rest in the inanner of collecting 

 the Plankton. The Hensen net and its 

 method of use are open to objections, and 

 filtration methods vary widely in their ac- 

 curacy and results. Experiments carried 

 on at the marine laboratory of the Rhode 

 Island Agricultural Experiment Station 

 ■seem to show that the collection and de- 

 termination of Plankton by a centrifuge is 

 Sb very rapid and accurate method, and that 

 the results read volumetrically on the gradu- 

 ated glass collector are of value when taken 

 in connection with the nature of the ma- 

 terial collected. The total percentage of 

 Planktonts obtained and their condition, 

 especially of the most delicate forms, far 

 surpasses any other method known to me. 

 The work has been carried on with the 

 Plantonokrit, designed and described by 

 Dr. C. 8. Dolley (Proc Acad. Nat. Sci., 

 Phila., May, 1896). The machine acts 

 upoua fixed quantity of water (2cans, each 

 of I litre capacity) . Nearly two years' work 

 with the method have given results suffi- 

 cient to warrant continued experiments. 



Note on Aseidian Anatomy. M. M. Metcalf. 



Neural gland. — ^A neural gland is pres- 

 ent in all groups of Tanicates, including 

 Appendicularice, Salpidce, Odacnemus. 



Its position. — In Appendicularicz, dorsal ; 

 in Simple Ascidians, dorso-lateral (^Molcjulidce) , 

 ■dorsal ( Cynthiidce) or ventral ; in Compound 

 Ascidians, dorsal {Botryllidce) or ventral ; 

 ventral in Doliolidce, Pyrosomidce, Salpidce and 

 Odacnemus. 



Its size. — Insignificant in Appendicularia ; 

 in Ascidians varies from a minute and nearly 

 fanctionless gland to a size fifteen times as 

 large as the ganglion ; in Pyrosoma and Salpa 

 small ; in Doliolum equal to the ganglion. 



Many Simple Ascidians have the gland 

 prolonged into the dorsal raphe, i. e., into 



the median portion of the pharyngeo-cloacal 

 septum. In most of these species merely 

 the duct of the gland is so prolonged ; in 

 other forms the raphe contains much glan- 

 dular tissue in connection with the duct- 

 In some species of Simple and Compound 

 Ascidians the tissue of the gland is continu- 

 ous with the cellular area of the ganglion, 

 recalling the way in which they both are 

 formed from a common structure, the vis- 

 ceral region of the larval neural tube. This 

 origin of the gland from the neural tube (as 

 described by Julin) is readily demonstrated 

 in Molgula Manhattensis and in Edeinascidia 

 turhinata. 



In all species studied the secretion of the 

 gland is formed by the degeneration and 

 disintegration of cells proliferated from the 

 walls of the duct or its branches. It is, 

 therefore, extremely doubtful if the gland 

 has any renal function. No concretions 

 were found. 



The condition of the gland is very differ- 

 ent in different species. The divergence 

 affects its size, position and shape. Portions 

 present in one species may be absent in an- 

 other species of the same genus. The 

 homology of the gland in Salpa with that of 

 the Ascidians is doubtful. 



Function of ciliated funnel. — It is not 

 merely the aperture of the duct of the 

 gland, for (1) it is often not connected with 

 the gland, though well developed (e. g., 

 Salpa), and (2) it has a rich innervation in 

 several species of Simple Ascidians and ap- 

 parently in some Salpas. In some species, 

 at least, it is probably a sense organ. 



The intersiphonal organs of Tunicates 

 show a remarkable asymmetry. Assuming 

 the sagittal plane of the ganglion to coincide 

 with that of the whole animal, the funnel is 

 on the right side, and so also is often the 

 whole or a part of the gland. 



In Molgula Manhattensis there is a great 

 semilunar fold of ectoderm that pushes into 

 the cloaca parallel to the pharyngeo-cloacal 



