Maech 5, 1897.] 



SCIENCE. 



391 



after fusion of the sperm-aster, a single 

 ' centrosome ' is found at the center of each 

 aster. In later stages the center of the 

 aster is occupied by a well-defined reticu- 

 lated sphere, somewhat smaller than is the 

 case after strong sublimate-acetic, and con- 

 taining a group of distinct intensely shining 

 granules (10-20 in number). The central 

 sphere often has a sharp boundary and 

 gives almost the appearance of a minute 

 cell nucleus. Whether this appearance is 

 normal remains to be seen, but the possibil- 

 ity must be born in mind that even related 

 forms may differ considerably in respect to 

 the morphology of the centrosome and 

 centrosphere. 



Ohservations upon Fertilization in Gasteropods. 



H. E. Ceampton, Jr. 



The observations were made upon a spe- 

 cies of Doris collected on the Pacific coast 

 and upon a species of Bulla from Wood's 

 Holl. A complete confirmation was ob- 

 tained of the accounts of fertilization given 

 by Wilson and Matthews, Boveri and Hill 

 upon sea urchins, Mead upon Chcetopterus, 

 Kostanecki and Wierjeroski upon Physa. 

 The sperm nucleus is preceded by the di- 

 vided centrosome, although an aster is not 

 formed till after the union of the germ 

 nuclei. The first polar spindle of the egg 

 has a double centrosome at the poles, while 

 the second maturation spindle bears but a 

 single centrosome at the pole. These, how- 

 ever, are very large, and the one remain- 

 ing in the egg finally breaks up, the centro- 

 somes of the cleavage spindle being derived 

 from the sperm. The germ nuclei never 

 fuse, but lie in very close contact to one 

 another. 



The Maturation and Fertilization of the Eggs of 



lAmax. E. F. Byrnes. 



After leaving the ovo-testis, the eggs of 

 Limax agrestis are stored in the albuminous 

 gland, where they are fertilized prior to the 

 formation of the capsules. 



By the time the egg reaches the albumi- 

 nous gland the first polar spindle is already 

 formed and occupies the middle of the egg 

 (the stage of the ' archiamphiaster'). 



The center of the egg-astrosphere appears 

 under widely different forms. In the stage 

 of the archiamphiaster it appears as a 

 central group of granules surrounded by two 

 sharply outlined, homogeneous envelopes, 

 an inner colorless envelope and an outer 

 deeply staining one. 



At the time of the formation of the first 

 and second polar bodies the center of the 

 astrosphere appears as a deeply staining 

 center, surrounded by an almost colorless 

 envelope from which the astral rays di- 

 verge. 



After the extrusion of the first polar body 

 it appears as a uniform finely granular 

 sphere in which two tiny centrosomes are 

 often distinguishable. 



After the extrusion of the second polar 

 body the center of the aster appears as a 

 large, clear, spherical structure, traversed 

 by a loose reticulum which connects, at the 

 center of the sphere, with a large, deeply 

 staining body. As the sphere increases in 

 size the central body fades out, giving 

 place to a reticulum which occupies the 

 entire sphere. The egg-astrosphere then 

 disappears. 



The sperm enters the egg at the lower 

 pole. As the sperm nucleus approaches the 

 upper pole it keeps pace with the growth 

 of the egg nucleus. 



The centrosome of the segmenting egg 

 enters the egg with the sperm, but the time 

 of the appearance of the sperm-asters is 

 variable. 



1. A New Microtome. 



2. Laboratory Methods. C. S. Minot. 



A new microtome was exhibited and its 

 mode of working described ; methods for 

 polishing the edges of microtome knives, 

 for storing pamphlets, and other matters of 

 laboratory administration, were pi-esented. 



