I06 MCMURRICH. [Vol. XI. 



of the yolk at this stage numerous cells just as in the forms 

 whose segmentation I have described, and it seems probable 

 that in Cymothoa the segmentation follows the centrolecithal 

 type, notwithstanding the large amount of yolk which is pres- 

 ent, the Q^g measuring about a millimetre in length with 

 a diameter but slightly less. 



In Ligia oceanica Nusbaum apparently believes that the seg- 

 mentation is of the discoblastic type, and Van Beneden ^ main- 

 tains the same view. So far as Nusbaum's observations are 

 concerned it must be pointed out that the material at his dis- 

 posal was hardly sufficiently representative of the earliest 

 stages to allow of perfect certainty on this point, and in view 

 of what certainly occurs in other Oniscidas a certain amount 

 of doubt as to the accuracy of his interpretation of the ob- 

 served phenomena is legitimate. My material, unfortunately, 

 is likewise too imperfect to settle the question, though the 

 earliest stage I have serves to emphasize the doubt. A section 

 through an egg of this stage is represented in Fig. 60, and 

 shows distinctly four nuclei and a fragment of a fifth, the pro- 

 toplasmic masses in which they are imbedded lying flush with 

 the surface of the yolk. In a surface view of the same (t^^ 

 before it was imbedded the nuclei were seen to be evenly 

 scattered over the surface, and in running through the series 

 of sections, which was complete, over eighty nuclei were 

 counted. There were none whatever in the interior of the 

 yolk, and none of the cells had separated from the yolk any 

 more than those figured. If the segmentation had been disco- 

 blastic one would expect to find some of the cells more or less 

 aggregated at one region of the egg but this does not occur, 

 and the appearance presented is identical with that found at a 

 somewhat earlier stage of development in Porcellio. Further 

 observation is necessary, I believe, before it can be definitely 

 decided whether the segmentation of Ligia is discoblastic or 

 superficial, i.e., centrolecithal. 



1 Van Beneden's paper, " Recherches sur la composition et signification de 

 I'oeuf," published in the Alhn. de PAcad. roy. dc Bclgiqiie, T. xxxiv, 1870, I have 

 not seen, the above statement being made on the authority of Korschelt and 

 Heider ('91). 



