SMALLWOOD : MATURATION OF HAMINEA SOLITARIA. 297 



as it is in Haminea. A definite spindle is always present between the 

 centrioles in the early stages of the longer or indirect process, and 

 usually in the shorter process also, — a condition which differs from that 

 found by MacFarland and Boveri (:0l), who hold that in Diaulula and 

 Ascaris it is formed only after the centrioles have moved apart a certain 

 distance; but it is in agreement with the account given by Conklin 

 (:0l) for Crepidula, although in the latter case the centrioles themselves 

 originate in a different manner. When the cytoplasm that immediately 

 surrounds the achromatic figure is studied (Plate 7, Figs. 46-49), no 

 specifically differentiated substance is noticeable even with high powers 

 of the microscope. The new spindle (mantle fibres) arises from the 

 cytoplasm in this region ; the granules which go to form the fibres may 

 begin to collect into lines before there is any direct physical connection 

 with the centrosome. The cytoplasm seems to take an active part in 

 causing these new rays to form, as if it had a ray-creating power. 

 Morgan (:00, p. 504) says: "The protoplasm, under the action of 

 strychnine, produces fibres that fill the egg. . . . All the rays converge 

 to the nucleus as a center." Boveri ('88) maintained that the granules 

 were formed into rays, but that they were aggregated about the centro- 

 some. The appearance of rays in Haminea is preceded by that of a num- 

 ber of distinct granules arranged in rows. It has already (pp. 288, 289) 

 been pointed out that the astral rays become granules as they undergo 

 disintegration. In the growth of the new rays the process is reversed. 



The spindle fibres, which arise in the cytoplasm, I have termed 

 " mantle fibres," because they are most abundant at the periphery of 

 the fine fibres which grow out from the chromatin. The derivation 

 of the mantle fibres from the cytoplasm agrees with the observations of 

 Hermann ('91), Moore ('95), MacFarland ('97), and others. The fine 

 fibres originating from the chromatin are surrounded by the mantle 

 fibres, and, I believe, take the place of the central spindle that has 

 disappeared. Agassiz and Whitman ('89, Plate 24, Figs. 1, 2, 3; 

 Plate 27, Figs. 1, 4) represent for osseous fishes conditions of the 

 spindle that are similar to those of Haminea (Plate 7, Pig. 49 ; Plate 8, 

 Fig. 54). The complete second maturation spindle, then, is composed 

 of cytoplasmic mantle fibres and an "axial " spindle, the fibres of which 

 are derived from the chromatin. 



One might at first thought imagine that the centrioles would pass 

 through similar phases in both the first and second polar spindles. 

 Such, however, is not the case. The centriole in the deep centrosome 

 of the second maturation figure is completed when the centroplasm is 



