46 SUMMARY OF CURRENT RESEARCHES RELATING TO 



at its hinder end, for there the largest ovules are found. The egg-cells 

 are developed along two bands, so that there really seem to be two 

 ovaries; this ^ is a somewhat, though not altogether, similar arrange- 

 ment to that described in Clavelina rissoana by MM. Van Beneden and 

 Julin. The ova are provided with follicular cells ; the author was not 

 able to follow out the development of the cells of the testa, but he in- 

 clines to Kowalevsky's opinion that they owe their origin to the folli- 

 cular cells. 



Structure of Pyrosoma.* — M. L. Joliet, in a posthumous memoir on 

 the structure and development of Pyrosoma giganteum, begins with a 

 partial bibliographical account of previous researches, from that of Peron 

 onwards. Then follows a diagnosis of the species :- — I. Pyrosomata 

 verticillata — P. elegans ; II. Pyrosomata paniculata — P. giganteum and 

 P. atlanticum. 



The anatomical portion is unfortunately incomplete ; the general 

 features are described, and then the external structure and disposition of 

 the component individuals, but after a brief note on the branchial sac 

 this section comes to an end. 



The blastogenesis is then discussed. As to the origin of the bud, the 

 author concludes as follows : — Between the extremity of the endostyle 

 and the epidermis there is a mesodermic layer which is continuous 

 beneath with the reproductive tissue ; the endostyle being prolonged 

 approximates this layer to the epidermis ; at this point the layer acquires 

 fresh cellular activity, and forms a continuous stratum of cells. In the 

 area of activity thickenings are produced which become the neural canal 

 and the peribranchial canals. As the bud grows, however, and rises 

 from its base, it loses thickness and cellular structure, and gradually 

 acquires the form of a delicate sac, including the scattered nuclei 

 which are seen almost throughout the adult. The organs which it 

 has produced — genital glands, neural and peribranchial canals, appear 

 isolated from one another. 



The next section is devoted to a description of the stolon. The fact 

 which rules the development of the bud is that its axis is not that of the 

 stolon, but is perpendicular to it. The transformations are described, 

 but must be followed on the plates. From the branchio-intestinal tube 

 there are developed — the digestive canal, the branchial sac, and the 

 inhalent orifice. Some details are added to the results of Huxley and 

 Kowalewsky on this point. The "hyaline organ", the branchial sac, 

 the " canal diapharyngien " which divides the latter into two chambers, 

 the peribranchial pouches, the formation of the cloaca, are then described. 

 An account of the heart and the respiratory apparatus completes the 

 whole of the paper which the editor could regard as finally approved by 

 the author. 



A final chapter, less finished but still valuable, describes the nervous 

 system. The ciliated sac is described, and its homology with the 

 "hypophysis" of Ascidians accepted and corroborated. It is main- 

 tained that in Pyrosoma " gland and canal develope at the expense of the 

 primitive vesicle, and the structure has thus quite a different origin from 

 the hypophysis of Vertebrates which is produced by an invagination of 



* ' Etudes anatomiques et embryogeniques sur le Pyrosoma giganteum, suivies 

 de recherches sur la faune de Bryozoaires de Koscoff et de MentoD,' Paris, 1888, 

 112 pp. (5 pis.). 



