ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 145 



Tunicata. 



Molgula ampulloides.*— Marc de Selys-Longchamps and D. Damas 

 have studied the anatomy and post-embryonic development of the 

 branchial sac in this Tunicate, and have also noted the relations of some 

 organs, e.g. the genitalia, in larva and adult. The youngest specimens 

 obtainable were already fixed, and had two pairs of protostigmata ; from 

 this stage onwards the development of the branchial sac takes place in 

 regular order from before backwards. The next stage possessed tbree 

 pairs t of protostigmata, which then, by the formation of horse-sboe-shaped 

 partitions, give rise to six pairs of secondary protostigmata. The early 

 or primary protostigmata, the authors believe to be formed by inde- 

 pendent perforations of the wall, and not to arise from one another. 

 As each of the six secondary protostigmata gives rise by division to new 

 stigmata, the innumerable stigmata of the adult may be conveniently 

 arranged in six series, each series having arisen from one of the 

 secondary protostigmata. The origin of these series is then described 

 in detail. 



In their examination of the adult, the authors have made out a 

 spherical corpuscle in the sub-neural gland, which appears to be the 

 persistent remains of a larval organ, apparently homologous with the 

 cerebral vesicle of other larval Tunicates. In regard to the development 

 of the genital organs, the most salient features are, the absence of a 

 duct morphologically equivalent to the vas deferens of other Tunicates, 

 and the absence of bilateral symmetry in the germinal epithelium. 



Development of Ciona intestinalis.f — Marc de Selys-Longchamps 

 has studied the development of the heart, the pericardium, and the 

 epicardia in this form, in order to settle the points at dispute between 

 Willey and Julin. He finds with Willey that the first rudiment of 

 the cardio-pericardial organ appears at a time when the mesoderm 

 has invaded the space between ectoderm and endoderm, but he is not 

 able to definitely decide the question as to its layer of origin. The 

 rudiment consists of two vesicles and is paired from the first. The 

 vesicles unite so as to present the appearance of a vesicle divided by a 

 double-walled septum. Towards the end of metamorphosis, the two 

 layers separate, the resulting cavity forming the heart. The cavities of 

 the two original vesicles form the pericardium, and the epicardia have 

 thus nothing to do with the origin of the heart. The latter do not arise 

 until the fixed Ascidian has undergone a considerable part of its de- 

 velopment, while the cardio-pericardial organ originates in the tailed 

 larva. The author thus strongly dissents from Julin's statements as to 

 the common origin of pericardium and epicardium. 



Structure of Ascidia. J — Prof. W. A. Herdman publishes an ex- 

 ceedingly clear description of a simple Ascidian, with a brief account of 

 the development, and a summary classification. Though professedly 

 based on previous researches by the author and others, and therefore not 



» Arch. Biol., xvii. (1900) pp. 385-488 (3 pis. and 2 figs.), 

 f Tom. cit., pp. 499-542 (1 pi.). 



% Trans. Liverpool Biol. Soc, xiv. (1900) pp. 34-88 (3 pis.). Also published 

 separately as Memoir I. of Liverpool Marine Biology Committee. 



April 17 th, 1901 L 



