ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 41 



two rows. The parapodia of Polychaeta are similarly derived, but the 

 archipodia first became more lateral. The sette of the Chaetopoda are 

 analogous with the " actinotrichia " or embryonic fiu-rays of fishes 

 and Sagitta : muscles pass to the bases of both these structures. In 

 Sagitta the lateral fin represents a fusion of parapodia. In fishes, 

 groups of actinotrichia fuse at their bases, and thus give rise' to the 

 branched fin-rays of the adults. The original continuous lateral 

 and median fin-folds were formed by a fusion of originally metameric 

 finlcts, just as the bases of the fin-rays of the skate fuse to form 

 propterygium, mesopterygium, and metopterygium. 



The lateral fins are formed from notopodial elements, the median 

 dorsal fin from fusion of two series of neuropodia, and the median 

 ventral from a similar fusion of notopodia. The Chordata and 

 Chaetopoda are two divergent series from an original stock. 



Development of Spermatozoa.* — Dr. G. von Wiedersperg con- 

 cludes that the spermatozoa are solely developed from the so-called 

 round testis-cells, the nuclei of which become the heads of the 

 spermatozoa, while the tail is formed within the cell. He accepts the 

 doctrine of Ebner that these round cells are the derivates of the con- 

 tinued division of the marginal cells, division in which commences 

 with a differentiation of the substance in the nucleus itself, the 

 chromatin becoming aggregated towards either pole.. It is peculiar 

 to this process of division that the two polar parts of the nucleus, as 

 they separate, still remain connected by more or fewer filaments, 

 which are ordinarily granular in appearance ; in this way the nuclei 

 of the new cells remain connected together by a bridge of fibres. A 

 study of the developing spermatozoa of the rat shows that the seminal 

 cells lie freely in the median cavity of the testicular canaliculi, sur- 

 rounded by a varying number of layers of other cells ; and these 

 develojjing cells are so disposed that in transverse sections we see 

 only one stage of development, and in a longitudinal section the 

 gradual passage of one stage into another. 



The nuclei present different characters at different stages; thus 

 in the young seminal cells they take colour just like the nuclei of- 

 their mother-cells ; in other forms the chromatin is completely 

 differentiated from the ground-substance. Later on no colourless 

 ground-substance is to be seen, and it appears, indeed, as if the 

 chromatin had become dissolved in it. The older the cell becomes 

 the less colouring matter does it take up. In some cases, as, for 

 example, in the African elephant, paranuclei are to be seen. 



In mature ejaculated sperm there are to be seen round cells, in 

 which the head of the spermatozoon lies by the wall of the cell, and 

 the tail, which has the form of an extremely fine filament, is likewise 

 applied to it ; in a larger number of cells the form was more or less 

 oval, the head projected far beyond the contours of the cell-membrane, 

 and the tail lay coiled up within the cell. Spermatocysts were also 

 found ; and there were others which were finely granulated, and executed 

 amoeboid movements, the processes being pale, club-shaped, spherical, 



* Arch. f. Mikr. Anat., xsv. (1885) pp. 113-36 (3 pis.). 



