416 RECORD OF CURRENT RESEARCHES RELATING TO 



With regard to the history of the velum the author is hardly more 

 in accord with well-known observers than he has shown himself up to 

 this point, for he states that the velum does not become converted into 

 the mouth-lobes, but undergoes gradual atrophy, and that the parts 

 which are said to be developed from it only appear at a later stage ; 

 similarly, Fol's statement as to the multicellular character of the 

 primitive kidneys is traversed, while M. Ganin's results are con- 

 firmed, and their unicellular character is illustrated by a figure. 



As regards the history of the development of the enteric tract — 

 The endodermal cells of the gastrula begin to take in spheres of deuto- 

 lecithin, which are formed in the albuminous spheres enclosed 

 in their cavity ; these spheres unite in each cell and form a dark- 

 coloured homogeneous mass. In all, five kinds of nutrient elements 

 may be detected : (1) Homogeneous vesicular drops, which are also 

 present in large quantities in the albuminous spheres ; (2) Spheres 

 with very small vacuoles inside them ; (3) Spheres with one large and 

 several small vacuoles ; (4) Dark non-vacuolated spheres, rich in 

 granules ; and (5) Spheres with a single homogeneous granule, which 

 is regarded as a modified cell-nucleus. 



It is, however, only a part of the endoderm which exhibits such a 

 metamorphosis of its cells ; at either end no change of this kind takes 

 place, but the constituent cells go to form the whole of the midgut ; 

 at one end the oesophagus is definitely fashioned, in such a way that 

 the primitive mouth (blastoj^ore, Lankester) corresponds to about the 

 cardia of the definite stomach ; this region is at first a solid cord of 

 endodermal cells. The anal invagination appears very early, on the 

 right side of the embryo and below the margin of the mantle ; the 

 enteron, the blind end of which has, by the coiling of the embryo, been 

 pushed towards the right side, comes into close contact with the pit ; 

 the mode of communication between them was not made out by the 

 author. The liver commences in the form of two blind sacs. In 

 somewhat later stages, the cells of the oesophagus and stomach are 

 provided with distinct flagella ; the mouth is encircled by large cells, 

 in which, however, it was not possible to detect flagella. In this 

 account the author makes no comparisons with the results of earlier 

 observers. 



Proceeding, next, to the account of the development of the nervous 

 system, we find that before there is any differentiation of the circum- 

 cesophageal ganglia, there appears in the cervical region a considerable 

 mass of large cells, which occupies the whole of the cavity above the 

 oesophagus, and has some of its cells placed below it ; the cells of the 

 mesoderm form an investment of connective tissue around it ; and dis- 

 tinctly mark it off from the surrounding parts. Its structure is 

 distinctly nervous in character. In the adult animal there is no trace 

 of this organ, and the author believes that it, with such other larval 

 structures as the velum, shell^gland, &c., disappears ; it may be known 

 as the emhryonic cerebral mass. The definite ganglia of the central 

 nervous system arise from local, though perhaps connected thick- 

 enings (never invaginations) of the ectoderm ; almost all the pairs 

 of ganglia are differentiated simultaneously, and are connected with 



