REVIEW, 93 



a sort of mulberry mass of nuciei has been produced. Occa- 

 sionally the nuclei are altogether absent. Most of the nuclei 

 contain a number of nucleoli, and their form as well as that of 

 their nuclei is excessively inconstant, varying from globular to 

 semilunar. 



In many of the cells, instead of, or in addition to the nuclei, 

 are found globular, sharply contoured bodies, containing finely- 

 granular protoplasm, vacuoles, and deeply-staining structures 

 resembling in some cases the nuclei, in others the nucleoli of 

 endodermal cells. The structures in question (well shown in the 

 cell to the left in fig. 6) have, in fact, all the characters of the 

 secondary mesoderm cells (s. ms.) scattered about the neigh- 

 bouring yolk. Some endoderm cells were observed which 

 were ruptured at the upper end, a number of these glo- 

 bular cells being congregated round the aperture then formed. 

 This appearance, however, may have been artificially pro- 

 duced. 



The exact mode of origin of these remarkable structures is 

 uncertain, but the appearances observed seem to show that the 

 nuclei of the endodermal cells surround themselves with accu- 

 mulations of protoplasm, become vacuolated, and so produce 

 a well-defined globular body, which passes out of the cell 

 into the surrounding yolk, acquiring a nucleus either before or 

 after becoming free. This endogenous method of cell formation 

 is one of the most interesting and unexpected points brought 

 out in Reichenbacli's paper. 



Towards the end of the Nauplius stage a considerable aggre- 

 gation of mesoderm cells takes place beneath the medullary 

 groove, producing a median cellular cord, which extends from 

 the anterior boundary of the procephahc lobes to the abdo- 

 minal process, dividing to pass round the gullet. This structure 

 bears a considerable resemblance to the " Wurmchorda^^ figured 

 by Semper in Nais and Ckatogaster, but as it is very variable 

 in difl"erent embryos, and extremely transient, disappearing by 

 the time the maxillse have appeared, it is quite possible that it 

 may be, as Reichenbach suggests, a mere accidental accumula- 

 tion of mesodermal cells. 



As to the further fate of the secondary mesoderm, Reichenbach 

 considers that it has to do with the formation of the blood. It 

 has, however, in embryos past the Nauplius stage, quite lost its 

 specific character. 



Reichenbach gives no figures or detailed descriptions of any 

 stages past the Nauplius. He gives, however, a short account of 

 the subsequent change in the yolk-devouring endoderm cells. 

 These continue their depredations upon the food material until 

 they have, as shown in fig. 8 (woodcut), completely eaten up the 



