4l8 MONTGOMERY. [Vol. XV. 



present in none of the ova, though here the same stages of 

 the ova were present as in the first individual. When they 

 occur it is only in the larger germinal vesicles. They are 

 apparently structures sui generis, and I have only the sugges- 

 tion to offer, that they might be characteristic of a particular 

 generation of egg cells, as their absence in the ova of some of 

 the individuals of the mollusc would render probable (compare 

 the observations of Hacker, 'ssa, where nucleolar differences 

 were found in the ova of primiparous and multiparous individ- 

 uals of Cyclops stremais). 



In Fig. 70 is a remarkable case depicted, namely, two small 

 nuclei lying within a larger germinal vesicle, the former having 

 apparently been assimilated by the latter. 



2. Doto. 



(Plate 22, Figs. 64, 68, 69.) 



The nucleolar differentiation of these ova is essentially as in 

 Montagua, so that no detailed description of the process need 

 be given here. But in the five individuals of Doto which were 

 sectioned, no traces of pseudonucleoli were seen, and the nutri- 

 tive globules within the nuclear sap are usually smaller and 

 much more numerous than in Montagua. The yolk globules 

 also have different shapes in these two genera.^ 



3. Ainphiporus glutinosus (Verr.) 

 (Plate 24, Figs. 140-158.) 



(For descriptions of the connective-tissue elements of the 

 nemerteans, from which the genital products are derived, cf. 

 my previous paper '96.) 



In the nuclei of the connective elements, by a differentia- 

 tion of which the ova are produced (without any intervening 



1 For the observations of other authors on molluscan germinal vesicles, cf. the 

 reviews of the papers of Wagner ('35, '39), Flemming ('74), O. Hertwig ('78b), 

 Lonnberg ('92), Balbiani ('65b), Platner ('86), Leydig ('55a, '50), Stauffacher 

 ('93, '97), Stepanoff ('65), Loven ('49), Mark ('81), List ('96), Blochmann ('82), 

 Trinchese ('80), Heuscher ('93), Hubrecht ('81), Carnoy ('84, '85), Wiren ('92), 

 Fol ('89). Lacaze-Duthiers ('57), Quatrefages ('49). 



