ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 411 



body — the " Nebenkern." An exactly analogous process is observed 

 in cases where the division of the protoplasm does not occur ; here 

 also the accessory body arises directly from the spindle-fibres. 

 Between the framework of the coil, the spindle-fibres, and the 

 accessory body, there is thus a genetic connection ; all three are 

 modifications of the same element. The process is probably as 

 follows. After the chromatin of the nucleus has divided into micro- 

 somata, these arrange themselves in regular curved rows ; the 

 accessory body enters the nucleus and forms the framework of the 

 coil ; the latter persists as the spindle-fibres, while the chromatin con- 

 centrates in the gTanular equatorial plate ; the spindle-fibres come into 

 direct connection with the protoplasm at the poles ; after division of 

 the chromatin substance, the resulting pole-plates form anew regular 

 nuclei, and the " anaphasis " either repeats inversely the stages of 

 the " prophasis," or the accessory nuclear body arises directly from 

 the spindle-fibres. Which of these two cases occurs depends upon 

 the degree in which the protoplasm is associated with the division. 

 Herr Platner adds some further remarks on the number and origin of 

 the elements of the equatorial gi-anular plate, and a critical notice of 

 recent contributions by Carnoy and Gilson. 



2. Oogenesis and Spermatogenesis in Arion. — The earliest stages 

 of the reproductive organ exhibit primitive sexual-cells, or rather 

 irregular nuclei imbedded in a homogeneous substance. In the 

 centre of the nuclei a formation of granules occurs, and a finely 

 granular protoplasm begins to be formed round about. These 

 elements increase considerably in number, and apparently directly ; 

 they form (a) primitive ova ; (b) spermatogonia and basal cells ; 

 (c) nutritive cells furnishing the yolk ; and {d) nuclei of the alveolar 

 wall and of the follicular membrane. The latter are reserve germs, 

 and form a new generation after the expulsion of the contemporary 

 sexual cells. The sexual cells in the alveoli are distinctly separable 

 into a peripheral layer consisting chiefly of ova, and a central zone 

 of spermatogonia. The latter are characterized by the presence of a 

 single large nucleolus, which appears along with the bent rods form- 

 ing the accessory body. The origin of the latter as an outgrowth 

 from the nucleus has been already described. Becoming gradually 

 roimded off", it exhibits a distinct membrane, and internally an 

 irregular distribution of chromatin over a network of faintly stained 

 strands. The ova are at first distinguished from the spermatogonia 

 only by their peripheral disposition, the greater development of their 

 protoplasm, and their much larger, more oval nucleus. A rapid 

 growth is the natmal result of the direct supply of abundant food 

 insured by their peripheral position. They increase in number in a 

 manner exactly analogous to that above described in the case of 

 Helix. Within the nucleus are seen not only the proper germinal 

 spot, of a roundish form, at fii'st interrupted by projecting elevations, 

 but another round body, which Platner terms the nucleolus. He 

 compares the presence of these two bodies with similar phenomena 

 observed by Leydig, Trinchese, Van Beneden, and V. la Valette St. 

 George. When the ova of Arion have attained their final form, the 



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