438 



SCIENCE 



[N. S. Vol. XXXIX. No. 1003 



lobe. The egg shows a high degree of organiza- 

 tion at an early stage. Whatever may be the sig- 

 nificance of the yolk lobe, it is an adaptation as- 

 sociated with early cleavage, apparently correlated 

 with the karyokinetic figure; it aids in producing 

 unequal cleavage; it isolates cell materials, so that 

 they are unaffected by early transformations of the 

 nucleus; and, in Cirratulus, it appears to aid in 

 the arrangement of the cell pattern. Conklin's 

 theory ( '12), that the yolk lobe is due to a weak 

 spot in the protoplasmic pellicle, through which 

 the lobe is forced out by "mitotic pressure," is 

 inadequate. For this theory would not explain the 

 non-appearance of the lobe in Cirratulus at the 

 third cleavage, though it appears in both earlier 

 and later stages. 



A Solution of the Problem of Yolh Manipulation 



hy Oplivura: Caswell GeavE. 



The egg of the brittle-star, Ophiura brevispina, 

 contains a very large amount of yolk and in its 

 cleavage and early development this yolk, in the 

 form of minute spherules, is equally distributed to 

 all of the cells. 



In its yolk distribution it, therefore, does not 

 differ from the eggs of other EchLnoderms but 

 does differ greatly from those eggs of Arthropods, 

 MoUnscs and Vertebrates which are rich in yolk. 

 In the latter, the yolk is early segregated either 

 into a few inert cells or into a portion of the egg 

 from which the active cells withdraw during de- 

 velopment. 



In consequence of the large amount of yolk in 

 the egg of Ophiura and of its equal distribution to 

 every cell during segmentation and early develop- 

 ment, a comparatively large amount of the energy 

 of the egg is expended in the manipulation of its 

 yolk content. For example: the resting cells of 

 the blastula have the form of slender prisms, 

 their length being to their breadth as nine is to 

 one. During its mitosis, however, each cell be- 

 comes approximately spherical in shape. Con- 

 nected with this enormous change in shape and 

 position of a dividing cell, there takes place a very 

 considerable readjustment of adjacent cells and 

 their contents and especially an entirely new ar- 

 rangement of the yolk spherules of the dividing 

 cell. 



The interesting observation herein reported is 

 that this expenditure of energy in juggling with 

 yolk spherules ceases when a stage in larval de- 

 velopment is reached in which the gut and ocelom 

 are differentiated. At this stage the cells ex- 

 trude practically all of their supply of yolk into 



the blastocoele cavity. The redistribution of this 

 mass of yolk to the tissues of the organism is a 

 function of amoeboid mesenchyme cells. 



CYTOLOGY 



The Nerve Centers of the Electric Organ in Baja 



Punctata: Ulrich Dahlghen. (Xllustrated 



with lantern slides.) 

 The X-element of Plymouth RocTc Fowls: M. P. 



GUTEB. (With demonstrations.) 

 Chromosomal Variations in the European Earwig, 



Forficula Auricularia: F. Payne. 



Spermatogensis in Chrysemys marginata and Cis- 



tudo Carolina: H. E. Jordan. 



Chromidia appear to originate in the sperma- 

 togonia by a process of extrusion of chromatic 

 particles from the nuclear recticulum. In 

 Chrysemys the chromosomes during early growth 

 stages are aggregated in or upon the nucleus; 

 from here they disperse as small paired granules 

 or rods; subsequently the chromosomes enlarge; 

 the typical synapsis figure is absent. The nucleolar 

 residue persists in part as a compact oval or 

 paired-rod element, suggesting an accessory chrom- 

 osome. The haploid number of chromosomes is 17, 

 including one larger U-shaped element which passes 

 apparently undivided (frequently as a pair of 

 rods) and in advance of the other chromosomes to 

 one pole of the first maturation spindle. In Cis- 

 tudo a typical synapsis figure appears; the haploid 

 number of chromosomes is 16; and there is no evi- 

 dence similar to that in Chrysemys suggesting an 

 X-element. Numbers of the secondary spermato- 

 cytes apparently divide amitotically, perhaps an 

 abnormal condition. 



A Microscopical Investigation of Tissues From 

 Dogs Which Fasted Extremely Long Periods of 

 Time: S. Morgulis, P. E. Howe and P. B. 

 Hawk. 

 The Germ-cell Cycle in Animals: E. W. Hegner. 

 Of the nine periods into which the germ cell 

 cycle in animals may be divided, two were dis- 

 cussed: (1) Cyst-formation in the testis of the 

 potato beetle, Leptinotarsa decemlineata, and (2) 

 the localization of the germ-cell substance in the 

 unsegmented egg. At a certain stage in the multi- 

 plication period the spermatogonia of the potato 

 beetle become each surrounded by epithelial cells. 

 Each spermatogonium dividos by mitosis and the 

 daughter cells can be identified because of connect- 

 ing strands — the remains of the spindle. These 

 spindle-remains enable one to prove conclusively 



