Miscellaneous. 335 



MISCELLANEOUS. 



Classification of the Peleci/jjoda. — Emendatory Note. 

 By B. B. WooDWAKD, F.G.S. &c. 



By an oversight, when rearranging Fischer's families of the 

 Pelecypoda to suit Pelseneer's classification, the Tancrediidae, which 

 by Fischer are placed between the Unicardiidte and the Donacidse, 

 were grouped with the former instead of with the latter. In the 

 table given, therefore, in the February number of the ' Annals,' 

 pp. 158, 159, the Tancrediidae should stand as Earn. 42 instead of 

 49, and the Earns, there numbered 42 to 48 should be 43 to 49. 



A Contribution to the Developmental Cycle of the Compound 

 Ascidians. By Johan Hjort, of Christiania. 



I. 



(1) Like Metschnikoff * and Delia Valle f I have always found 

 that the earliest rudiment of the bud of Botrylliis is in the shape of 

 a two-layered vesicle, of which the inner layer proceeds from the 

 parietal layer of the peribranchial cavity, while the outer one is 

 derived from the ectoderm of the larva. I have never been able to 

 confirm the repeated assertions of Giard J and Herdman § that in 

 the Botryllidae a " stolonial " gemmation occurs, in that the buds 

 are produced from the stolons of the mantle. Owing to the veiy 

 numerous transitional stages it is even possible to explain the 

 usually widely separated buds of colonies of Botryllus as having 

 arisen in consequence of a " pallial " gemmation. While, however, 

 Delia Valle regards the inner vesicle of the bud-rudiments which 

 is formed in the course of this pallial gemmation as endodermal, I 

 myself feel bound, in accordance with the investigations of Kowa- 

 levsky || and Van Beneden and Julin % and studies recently made 

 by Willey **, to consider this vesicle as ectodermal, since, according 



* " Entwicklungsgeschichtliche Beitrage," Melanges Biologiques tir^a 

 du Bull, de I'Acad. de St. P(5tersbourg, t. vi. 



t '' Sur le bourgeonnement des Ascidies couiposees," Archives Itali- 

 ennes de Biologie, 188:2. 



X '' Rechevches sur las Ascidies compost5es," Archives de Zoologie 

 expeiimentale, 1872 ; also ' Oomptes Rendus,' 1891. 



§ Report of the ' Challenger ' Expedition, vol. xiv. 



II " Weitere Studien iiber die Entwicklung der einfachen Ascidien," 

 Archiv f. mikr. Anat. 7 Bd., 1871. 



•] " Recherches sur la muiphologie des Tuniciers,'' Archives de 

 Biologie, t. vi., 1886. 



** "On the Development of the Hypophysis in the Ascidians," 

 Zoologischer Anzeiger, xv. Jahrg. no. 400, pp. 332-334. 



