Bibliographical Notices. 381 



The infraoesophageal arm-nerve resembled even more a concen- 

 tration of the fibrous prolongations of these multipolar cells than a 

 well-defined nerve ; the latter are therefore considered as nervous 

 elements, distributed in the arm- walls and probably connected as 

 follows — those of the supraoesophageal nerve with the high epithe- 

 lium of the brachial groove and fold, those of the infraoesophageal 

 with the muscles of the cirri. 



On transverse sections, the infraoesophageal centrum was found 

 to consist of two longitudinal masses of small ganglionic cells con- 

 nected by a broad median commissure of nerve-fibres. This was 

 called by Hancock the median ganglionic mass ; and it is, indeed, not 

 quite destitute of nerve-cells. 



No ganglionic plexus was to be found in the mantle ; nor was the 

 author able to find any trace of the auditory sacs mentioned by 

 Morse as occurring in Lhv/ula, 



In the investigated species the sexes were found to be separated. 

 The generative organs were investigated ou transverse sections ; and 

 special attention was given to their young tops. The lamella con- 

 necting the glands with tho body-wall was found to be nothing but 

 an excrescence of the mesenchymatic layer of this wall, on which 

 the coelomic epithelium continued uninterrupted and unchanged. 

 At the free edge of this supporting lamella an irregular cavity was 

 found, forming a longitudinal canal (Hancock's genital artery). The 

 walls of this canal made many folliculiform evaginations, which at 

 their free surface were covered by the germinal epithelium. In the 

 testes this consists of thick masses of small cells with relatively 

 enormous nuclei. These masses by their bulk and number form a 

 continuous layer around the central cavity. Outside of this another 

 layer was found, consisting of much smaller cells, many of which 

 already show the caudal filaments of spermatozoids, while their 

 nucleus forms the head of them. The masses of germ-cells at the 

 tops of the evaginations gradually pass into the simple epithelial 

 layer of their walls ; and this layer is only a continuation of the 

 ccelomic epithelium of the supporting membrane. At the growing 

 tops of the testes nothing but a solid mass of undifferentiated cells 

 was found, showing in its centrum a small lumen, and connected 

 with the body-wall by a small lamella, the epithelium of which 

 passes uninterruptedly into this cell-mass. 



No membrane surrounds the germinal layers of the testes; the 

 spermatozoids therefore, when ripe, must fall into the body-cavity. 



In the ovary the evaginations of the supporting membrane are 

 covered all over with egg-cells in different stages of development. 

 Many were enveloped by a follicle of flattened cells : and these eggs 

 showed a large nucleus and a finely granulated protoplasm : others 

 were destitute of such a follicular membrane ; and in this case the 

 nucleus was generally also wanting or very rudimentary, while the 

 plasmatic granules were much coarser. The latter cells, which oc- 

 curred in all shapes, are considered as on the way of resorption. 

 Between the distinct egg-cells many small germinal cells were 

 found, from which, not only the eggs themselves, but also their fol- 



