67 



Accordingly the production of spermatoblasts cannot take place 

 equally on all sides but only at the free side, viz. that turned 

 towards the lumen of the follicle. This explains the difference of the 

 two types so far as the central and eccentric position of the blastophor 

 in the respective cases, is concerned. But further than this, it appears 

 that the nucleus of the eccentric sperm-blastophor of Helix and Rana 

 corresponds to the nucleus of a distinct testis-cell of Lumbricus. The 

 free spermatospores of Lumbricus are formed by division of parent cells 

 in the growing base of the small lamelliform testis. The sister-cell of 

 a free spermatospore is in this case left behind in the testis ; in Helix 

 and Mana there is no such division and liberation of the spermato- 

 spores. In these latter it is not until the spermatoblasts are fully formed 

 that they break away together with a basal mass of protoplasm from the 

 wall of the crypts and float in its lumen leaving the nucleated portion 

 of the sperm-blastophor adherent to the wall, and carrying a consi- 

 derable non-nucleated mass of the cell-body away with them. It is 

 then this non-nucleated moiety which strictly corresponds with the 

 central non-nucleated blastophor of Lumbricus : whilst the nucleated 

 moiety which still adheres to the wall of the testicular crypt and carries 

 on the development of spermatozoa again — in a succeding season — 

 is the representative of the sister-cell remaining in the testis of Lum- 

 bricus from which at a quite early period the free-floating spermato- 

 spore of that animal (and of many others which conform to the same 

 type) is separated by fission. 



The existence of the non-nucleated mass of protoplasm, centrally 

 or eccentrically placed and carrying the sperm-buds or spermatoblasts 

 and to which I have given the name of the sperm-blastophor 

 appears to be general in its occurrence in a wide range of animal forms. 

 The spermatoblasts growing as nucleated cells on the surface of this 

 blastophor are the essential and only important portion of the result 

 brought about by the developmental changes of the spermatospore or 

 primary sperm-cell ; the blastophor itself shrivels and is destroyed when 

 the spermatozoa drop from its surface in a ripe condition. 



London, December 1879. 



4. Medusen werden durch Frost getödtet. 



Von Dr. Karl M ö b i u s , Prof. in Kiel. 



Am 21. Dec. 1879 bemerkte ich beim Schlittschuhlaufen auf der 

 Kieler Bucht eingefrorene Medusen [Aurelia aurita L.) . Ihre Scheiben 

 lagen wohl erhalten im klaren Eise. Die Genital taschen waren deut- 



