254 MR. F. D. DYSTER ON PHORONIS HIPPOCREPIA. 



under the integument, and is not ciliated. The ova lie in its upper and visible portion 

 for some hours, vibrating backwards and forwards under the influence of the wave of 

 blood in the haemal vessel. They are ch-iven slowly upwards, tiU they arrive between 

 the two ducts which appear as ridges under the rami of the lophophore. The oviduct 

 here seems to contract in its dimensions ; and the ova assume a cylindrical form. They 

 pause here for about half an hour ; but at length the upper end of the cylinder dips sud- 

 denly down\vards, passes into the hollow ridge, and then mounting through it, is dis- 

 cliarged in a spherical form into the space between the inner tentacles, to which the 

 ova adhere by a glutinous exudation. They are voided alternately through each ridge, and 

 form a compact white mass, separable only with considerable difficulty, on each side of 

 the space in the concavity of the horseshoe, shadowed over by the interlacing extre- 

 mities of the inner tentacles. They vary in number from 10 to 80. When first extruded, 

 they are granular with a clear margin, and show the usual germinal spot on pressure. 

 In a few hours, cilia are developed aU over the surface ; and two depressions appear on the 

 circumference, indicating a cu'cular groove. This groove rapidly deepens ; and within 

 twenty-four hours the young exhibit distinctly a cephalic and an abdominal segment ; ante- 

 riorly the line of separation deepens ; and the abdominal portion becomes concave on tlie 

 upper surface, alternately receding from and embracing the convex surface of the cephaMc 

 portion which lies above it. The cilia increase in length and power ; and very soon, in 

 certain positions, the alimentary canal becomes distinguishable. The cephalic segment 

 divides into three lobes, of which the lateral are the longest and anterior, the central 

 highest and posterior. The larva has now great power of locomotion, and quits the 

 parent-nest when about forty-eight hoiu's old. 



The principal point of interest in the Fhoronis is the indubitable presence of blood- 

 corpuscles in proper closed vessels of the chculatory system. Von Siebold * is obscure and 

 brief on this subject, and simply says — " the blood of the Annelids ... is composed of a 

 liquid containing globules . . . which are always colourless and of a spherical form." 

 Milne-Edwards t says that, in the Vertebra ta, " la couleur rouge du sang est due aux glo- 

 bules que ce liquide charrie ; chez les A''ers a sang rouge, c'est en dissolution dans le hquide 

 lui-meme, que se trouve la mati6re colorante. . . . Les globules ne jouent dans cette colora- 

 tion aucun r61e essentiel, et d' ordinaire ces corpuscules paraissent meme manquer compl^te- 

 ment dans ce liquide. . . . M. de Quatrefages a ^te meme conduit a penser que dans I'im- 

 mense majority des cas,le sang rovige desAnnelides est completement prive des globules quel- 

 conques. II n'a rencontre qu'une exception a cette regie, et elle lui a ^te fouruie par une 

 espfece de Glycfere des c6tes de la Manche, chez laquelle il a trouv6 des globules rouges et de 

 forme discoide, nageant dans un liquide incolore. Mais M. Williams J, qui a public r^cem- 

 ment une serie nombreuse d' observations sur le fiuide nourricier des animaux invert6br6s 

 affirme que cette exception n'existe pas ; que les globules rouges decrits par M. de 

 Quatrefages se trouvent dans le Uquide de la cavity g^n^rale du corps, et non dans les 

 vaisseaux sanguins, et que dans aucun Ann^lide le sang proprement dit (ou sano- color^) 



* Von Siebold, Comp. Anatomy, translated by Burnett, vol. i. p. 1C8. 



t Le9ons sur la Physiologie, tome i. pp. 106-108 et note. 



X On the Blood proper and Chylaqueous Fluid of Invertebrate Animals. — Philosophical Transactions, 1852, p. 632. 



