232 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



2. Nucleoli, or Karyosomes. 



After the formation of the second polar cell the egg-nucleus becomes 

 vacuolated, and in most of the cases that I have observed the sperm- 

 nucleus also becomes vacuolated at the same time. Both contain many 

 nucleoli or karyosomes varying in size and situated either at the cross- 

 ing of linin fibres or arranged along such fibres in bead-like fashion. 

 The nucleoli frequently stain with varying intensity in the same nucleus, 

 but generally the staining of all nucleoli is very faint. The larger ones 

 appear to be vacuolated. I have no doubt of the integrity of these 

 karyosomes as distinct elements. Platner ('86) believed them to be 

 distinct elements; but the opposite view was maintained by Boveri 

 ('90, p. 357). who is inclined to think that Platner's " Karyosomen " 

 are artefacts produced by a crowding together of net-knots and numerous 

 large achromatic nucleoli by an unfavorable method of preservation, and 

 that the mistaken interpretation is in part due to the appearance given 

 in very thin cross-sections. I believe, however, that the structures in 

 question can be shown to actually exist as distinct normal bodies, not 

 artefacts. Moreover, I can bring observations to support Platner's 

 claim that the chromosomes which are taking shape for the first cleav- 

 age spindle are to be seen surrounding karyosomes as rings. Platner 

 ('86, p. 53) says, " Die Karyosomen nur erscheinen auf den ersten Blick 

 vollig farblos, eine aufmerksame Beobachtung lehrt aber dass die Chroma- 

 tinsubstanz welche anfangs difFus in ihnen vertheilt war, sich in der 

 Form kleiner Kornchen an der Peripherie concentrirt hat." 



"Diese Chromatinelemente sind anfangs noch sehr klein und in 

 grosserer Anzahl vorhanden und entzishen sich dann leicht der Beobach- 

 tung. Spater sammeln sie sich aber z'u einigen wenigen grossern Kor- 

 pern an und treten dann deutlich hervor. Von diesen Chromatinkornern 

 enthalt die Mehrzahl der Karyosomen zwei Stiick, welche meist an zwei 

 diametral gegeniiberliegenden Punkten der Peripherie gelegen sind. In 

 den kleinern erkennt man zuweilen nur ein seiches Element." 



I have not studied the karyosomes sufficiently either to confirm or 

 deny Platner's quoted statement, that the chromatin is diffused through 

 the karyosomes preceding the time of its accumulation into a ring on 

 tiie periphery. I should say, however, that the fact that the karyo- 

 somes show staining reaction before the chromatin is collected on the 

 periphery, and that afterwards they do not (a statement which I have 

 not quoted), is not absolute proof that the chromatin is contained in the 

 substance of the karyosomes. The variations in the staiuability of these 



