70 MR. W. K. BROOKS ON LUCIFER: 



that it is difficult to trace any resemblance to the various forms of segmentation which 

 occur in other groups of animals. In Lucifer the case is reversed, and we have a type 

 of segmentation which is obviously similar to that of the Echinoderms, Annelids, 

 Molluscs, Tunicates, Vertebrates, &c., but is less obviously related to that of the eggs 

 of closely allied forms. The resemblance to what may be called " normal " segmenta- 

 tion is so plain that it need not be dwelt upon, but the relation between the egg of 

 Lucifer and an ordinary centrolycethal egg is by no means clear. 



It seems probable, however, that since the food -material which has not been assimi- 

 lated becomes centralised, after segmentation is somewhat advanced, in the single 

 spherule c, of fig. 11, this spherule must correspond to one of the yolk-pyramids of an 

 ordinary Crustacean egg. This then divides, by radial fission, into two portions (fig. 

 13, c), and it seems probable that the food-material then becomes restricted to their 

 central ends, while the outer protoplasmic ends separate off as a pair of blastoderm 

 cells (fig. 15), thus leaving the two masses of food-yolk (c) inside the segmentation 

 cavity. While I was investigating the subject I regarded the spherule c, of fig. 11, 

 as a primary mesoblast, which became pushed into the segmentation cavity, and then 

 divided up to form the mesoderm ; and I expressed this view without comment 

 in a preliminary abstract of the subject (" Embryology and Metamorphosis of the 

 Sergestida?," Zoologischer Anzeiger, iii., p. 563). In most cases where the origin of the 

 mesoderm has been most carefully studied, it originates by the separation of the inner 

 ends of the cells which are to give rise to the endoderm, either before or during or 

 after the invagination takes place ; the mode of origin of these spherules in Lucifer 

 and their position in the egg agree with what we should expect if thej belong to the 

 mesoderm, but the great quantity of food -material which they contain would hardly be 

 looked for in this case, and favours the view that they are yolk-pyramids rather than 

 mesoblasts. 



As I examined no eggs between fig. 20 and fig. 21, the later history is uncertain, but 

 a reference to figs. 21, 22, 23, and 24, which are about twenty hours later than fig. 20, 

 shows that the region of the digestive tract of the Nauplius is marked by the presence 

 of a number of large polygonal masses of what appears to be food-yolk, and it seems 

 probable that these are the derivatives of the spherules c, of fig. 20. I was not able 

 to actually witness the change from fig. 11 to fig. 15, and cannot state with absolute 

 certainty that the spherules c divide into a central and a peripheral portion. Fig. 1 5 

 seems to indicate that this is the case, but in the absence of direct observation of the 

 change, it is possible that the two cells which in fig. 15 lie below the cells c, are the 

 ones which were at its sides in fig. 1 1 . 



If each of the cells c gives rise to a blastoderm cell, we shoiild expect to find two 

 more cells in fig. 15 than in fig. 18, but the number is the same. This is hardly a 

 safe guide, however, for while the drawings are careful copies from Nature, they are 

 not from the same egg, and the cells are so wedged together that vertical sections in 



