592 SUMMARY OF CURRENT RESEARCHES RELATING TO 



buccal cavity, and, just as in the Ascidians, this orifice is placed in 

 the middle line, immediately in front of the boundary line between 

 the primitive buccal cavity and the anterior cul-de-sac of the digestive 

 tube. In both cases the organ is well supplied with blood-vessels, 

 and that of the Ascidians, just as that of the Vertebrates, appears to 

 be epiblastic in origin. 



10. The hypoj)hysial tubercle has not, as has been supposed, any 

 olfactory fimctions ; no nerve goes to it, and there are no olfactory 

 cells. 



11. The body-wall of an Ascidian may be regarded as formed of 

 the same parts as that of Amphioxus. Below the integument there is 

 a layer of connective and muscular tissue, on the inner face of which 

 we find the external epithelium of the peribranchial cavity. 



The author concludes by giving a synonymic table of the terms 

 applied to the different parts of the Ascidian here under discussion, 

 and divides it into two halves, one anatomical and one artificial. The 

 number of artificial terms is in some cases appalling, as may be seen 

 from what is anatomically called the dorsal raphe. Among other 

 terms this part has been known as the anterior vessel (of Savigny), 

 the hypopharyngeal band (of Huxley), the posterior vibrutile groove 

 (of Fol), and the posterior raphe (of Lacaze-Duthiers). 



Development of Lithonephria.* — In describing the embryogeny 

 of this Ascidian, M. A. Giard points out that the study of it is 

 facilitated by the fact that the ova are incubated by the parent, and in 

 such a way that various stages may be found in one individual. He 

 finds that the " cells of the green layer," or " granulosa Zellen," have 

 an origin outside the ovule ; they have migrated from the follicle, and 

 penetrated into the yolk ; and they are in no way developed from the 

 germinal vesicle. Soon they swell, and their contents divide into six 

 protoplasmic masses, their wall disappears, and they are slowly driven 

 to the periphery of the egg. There is, owing to the abundant yolk, a 

 remarkable condensation of the developmental history of this form. 

 At stage " VIII." there are four coloured endodermal and four 

 colourless ectodermal cells. At stage "XXXII.," and even before 

 it, the egg distinctly exhibits the bilateral symmetry of the adult ; at 

 the nutrient pole there are two large and four small endodermal 

 blastomeres ; at the base of the two large ones six mesodermal cells 

 form half an equator, three on each side. At the formative pole 

 there are twenty cells forming an ectodermal hemisj)here ; the meso- 

 dermal cells are of an endodermal origin. By epiboly the mesoderm 

 becomes covered by the ectoderm ; the half equator becomes horse- 

 shoe-shaped. This is the rudiment of the notochord, which in ova 

 that undergo equal segmentation appears so much later. The author 

 points out that he has previously insisted on the fact that the stages 

 from IV.- VIII., which physiologically represent a morula, mor- 

 phologically represent a gastrula. Here he finds that up to stage 

 XXXII. the egg is still a morula physiologically, although there is 

 a mesoderm developed, and he thinks that embryonic condensation 



* Comptes Eendus, xcii. (1881) pp. 1350-2. 



