272 



SCIENCE 



[N. S. Vol. XXXIII. No. 842 



stages, but during synapsis a dark-staining 

 snarply contoured body (accessory chromosome) 

 appears at point where the loops converge. This 

 point is always next the conspicuous centrosphere 

 lying just outside of the nuclear wall. Plasmo- 

 some believed to become accessory chromosome 

 on basis of similarity of form, i. e., bipartite 

 character. In post-synaptic stages, while the 

 autosomes are still only slightly chromatic, the 

 deeply chromatic monosome (accessory chromo- 

 some) always lies close to point where centro- 

 sphere is located. 



Equatorial plates of first maturation mitosis 

 contain nine chromosomes (eight bivalent ordi- 

 nary and one accessory chromosome ) . The acces- 

 sory, both here and in earlier stages, appears 

 bipartite, sometimes completely divided and sepa- 

 rated. The accessory passes undivided to one 

 pole slightly in advance of the eight univalent 

 ordinary chromosomes, the opposite pole receiving 

 only eight chromosomes. Two types of secondary 

 spermatocytes are formed, one with a slightly 

 chromatic nucleolus ( =z accessory ) , the other 

 without. Equatorial plates of second maturation 

 mitoses show five chromosomes (four pairs of the 

 eight univalents of last mitosis + one accessory) 

 and four curomosomes, respectively. In late telo- 

 phase the pairs are again resolved into nine and 

 eight chromosomes, respectively. Dimorphism of 

 spermatids — metamorphosis into spermatozoa and 

 the presence of ohromidial elements — were also 

 considered. 



This paper will be published in the Journal of 

 Morphology. 



The Formation of the Spermatophore in ArerUoola 

 and a Theory of the Alternation of Generatio^is 

 suggested by the Facts in the Case: EixioT E. 

 Downing, Northern State Normal School, Mar- 

 quette, Mich. 



The spermatophore in Arenicola cristata arises 

 as a result of the cleavage of a primary sperma- 

 togonium in a manner homologous with the 

 cleavage of an egg in the same species. There is 

 an invagination of certain spermatogonia! macro- 

 meres and micromeres to form the nutritive cells 

 which supply the developing spermatophore with 

 food by their disintegration and absorption. 

 These cells are homologues of the egg mes- 

 entomeres. The spermatophore is shed from the 

 testis into the body fluid at an early stage, some- 

 times even before the cleavage of the spermato- 

 gonium has begun. Here the early spermatophore 

 becomes a hollow mass of cells which later, by a 

 false invagination, becomes gastrula-like. The 



false gastrula flattens out and becomes a saucer- 

 shaped mass of spermatids. These develop within 

 themselves the sperm. 



The facts suggest that the spermatophore is an 

 individual — the gametozoon which bears the 

 gametes. The adult male is a sporozoon which 

 develops the spores or primary spermatogonia. 



The alternation of generations and reduction 

 are independent phenomena, as is shown ( 1 ) by 

 apogamy and apospory, (2) by the fact that 

 among the protozoa and algse reduction may occxa 

 before, during or after the conjugation of the 

 gametes, that is, in either the sporo- or gameto- 

 generation. 



Reduction is an adjunct rather than a corollary 

 of sexuality. If it were the latter, reduction 

 should always occur in a definite relation to the 

 sexual act, not before, during or after it. 



The spermatophore must be suggestive of the 

 primitive animal type just as the gametophyte 

 suggests a thalline ancestry for plants. Perhaps 

 the Volvocales come nearest, among living forms, 

 the primitive form. In Volvox reduction has its 

 animal position during gametogenesis. 



If reduction occurred in the primitive forms 

 before or during the fusion of the gametes the 

 gameto- and sporo-generations would have the 

 same number of chromosomes. This is the case in 

 the gametozoon and sporozoon of Arenicola. 

 Since all animals and many algce have reduction 

 in such a position the preponderance of evidence 

 is that it had this position in the common animal 

 and plant prototype. In plants, then, it has 

 shifted from this primitive place toward the end 

 of the sporophyte generation. 

 Aquatic Photography for Zoologists: Wm. Aian- 



SON Bbtan, Honolulu, H. I. 



The paper briefly explains and illustrates with 

 lantern slides some of the essentials in the method 

 and the apparatus used in securing photographs 

 of aquatic objects for book and class-room illus- 

 tration. The successive steps in evolving a 

 method that resulted in securing the first aquatic 

 motion pictures are explained. 

 The Discovery of Arohigetes in America, with a 



Discussion of its Structures and Affinities: 



Henbt B. Wabd, University of Illinois. 



Among the monozoic cestodes, often grouped as 

 a separate class or subclass under the name 

 Cestodaria, the Caryophyllseidse stand closest to 

 the merozoic cestodes, particularly to the Bothri- 

 ocephalidse. Neither of the genera previously 

 known, Caryophyllwus or Archigetes, has been 

 reported from this continent, although several 



