564 RECORD OF CURRENT RESEARCHES RELATING TO 



of the Danube ; the earlier stages appeared to be very similar to those 

 of Lumhricus ; the mesoderm is first represented by two large cells, 

 whicli persist for a long time, and the ectoderm by three large cells, 

 which occupy the anterior end, the dorsal surface, and the sides of the 

 embryo ; the two mesodermal cells grow out into a row of cells on 

 either side, for which the term of '• mesodermal stripes " is now 

 proposed ; the old term " germ-stripe " has been used for so many 

 different sets of organs that a more accurate terminology seems indeed 

 to be justifiable, and for it the name " embryonic stripe " (or streak) 

 is now proposed. In the process of histological differentiation the 

 cells of the ectoderm become more clear, but the three large cells, 

 already spoken of, remained filled with dark, coarse granules ; albumen 

 is rajiidly ingested, and as a consequence the cells of the ectoderm and 

 of the mesodermal stripes increase greatly in number ; of the latter 

 two rows appear shortly after the development of the oesophagus, and 

 the two primitive cells become more separated from one another. It 

 is in the same layer that segmentation is first seen, and in it only ; 

 this process begins in the most anterior region, and is soon followed 

 by the development of the different organs; still the two primitive 

 cells go on dividing, and so adding to the mesodermal stripes. Co- 

 temporaneously with this the cephalic region, which is characterized 

 by the presence of a ciliated groove, which persists till development is 

 all but complete, develops a cavity, which is at once distinguished from 

 the coelom or body-cavity by its origin from the separation of the 

 ectoderm and endoderm, and not by the cleavage of the mesoderm ; 

 it is also single, and not double ; the mouth, with its gullet, and the 

 supra-oesophageal ganglia become developed, and this nervous region 

 gradually separates from the ectoderm, although it for a long time 

 remains connected with it in its most anterior portion. 



The primitive segments are formed by the separation of parts of 

 the mesodermal stripes, which form small multicellular and quad- 

 rangular plates ; a single layer of cells from them forms the enteric 

 fibrous layer, the most anterior and the most posterior layer form the 

 dissepiments of the now developing coelom, and the outer portion 

 becomes converted into the rudiments of the segmental organs and of 

 the setfe ; the former set of organs commences with one large cell in 

 each segment, which is connected with a row of smaller cells, which 

 extend into the next segment ; these all become differentiated into 

 three parts, the two terminal straight, and the middle one looped ; 

 while the whole apparatus leaves the ectoderm to take a deeper posi- 

 tion in the body. These segmental organs are found in all but the 

 first trunk-segment, but even in this Dr. Hatschek has observed a 

 collection of cells which disappear later on, but which would seem to 

 be similar in character. The more final stages of this form are not 

 described, as they differ in no important points from what is already 

 known to be the course of development in Lumbricus. 



Polygordiiis. — With regard to this somewhat enigmatic creature, 

 it is interesting to be reminded of Schneider's discovery of the fact 

 that the so-called " Lovenian larva," first described by Professor Loven 

 in 1842, and since examined by Professor Alexander Agassiz, is without 



