202 bulletin: museum of comparative zoology. 



They found the resting nuclei double, and sometimes the spindle was 

 double and the chromosomes in two distinct groups. They believed 

 there were thus represented in the cleavage nuclei maternal and 

 paternal elements which remained distinct. Conklin (:01) gave the 

 same interpretation to double nuclei found in Crepidula during the 

 telophase of mitosis, and sometimes continuing throughout the resting 

 period. The nuclei were typically composed of two vesicles, each 

 with a nucleolus, though the vesicles and nucleoli sometimes united 

 and thus became single. This condition he found in nearly all stages 

 up to that of 60-cells. Hacker (:03) carried his earlier investigations 

 on Copepoda further, and described the separateness of the two portions 

 of the nucleus in all stages of rest and mitosis, from the fertilized egg 

 to the germ mother cells. In Triton, Rubaschkin (:05) never found 

 two nucleoli in any resting nucleus; but in early cleavages he occa- 

 sionally found double nuclei in resting stages, though not during 

 mitosis. In the 16-cell stage and later (i. e. about the blastula stage) 

 he found two vesicles in the resting stage. During mitosis the spiremes 

 formed synchronously in the two vesicles, and for a short time after 

 the nuclear membrane was lost the chromosomes remained in two 

 ill-defined groups; but in the equatorial plate they constituted a single 

 mass. In some blastulae he found no double nuclei in any cell, and in 

 others there were three vesicles, which remained distinct for as long a 

 time as double nuclei did. Because of the et[uality of the vesicles in 

 size, and their synchronistic differentiation, he believes they represent 

 maternal and paternal constituents. Dublin (:05) found the somatic 

 nuclei of Pedicellina typically univesicular, but with two nucleoli, 

 which were symmetrically placed in the nuclei. This, in his opinion, 

 is not an indication of the autonomy of sperm chromosomes and egg 

 chromosomes. He is undoubtedly justified in refusing to accept the 

 presence of paired nucleoli as evidence of autonomy, but he seems to 

 me to go too far in saying, that in other forms bilobed nuclei probably 

 represent only an intermediate stage in the fusion of several vesicles 

 into one resting nucleus. This, of course, does occur, and possibly 

 may be true in some cases where gonomery has been claimed, but 

 probably not in all; it is distinctly not the case in Tubularia. As 

 already described, the daughter nuclei are double when in process of 

 re-forming, and remain so until the next spindle is produced, and even 

 then the chromosomes may be in two fairly separate groups. 



The case in Tubularia would seem to be a good example of persistent 

 gonomery, but what Dublin says (p. 354) in regard to Pedicellina, — 

 viz: that in early cleavages, where autonomy should be most marked. 



