432 Dr. F. Muller on the Seminal Fluid of lautliina. 



for carrying on such an investigation as this ; and when I was 

 able to resume it, I found that my whole stock of material had 

 become useless in consequence of the commencement of decora- 

 position. 



In the vicinity of the conical point several little lobes, resem- 

 bling narrow cilia, separate from the membrane. While the 

 structure is swimming, these little lobes oscillate rapidly and 

 strongly, and the whole membrane is in lively undulating move- 

 ment. When towed along by this singular swimming-apparatus, 

 the tail always appeared to me to be perfectly quiet ; the whole 

 structure, from the conical apex of the undulating membrane to 

 the rounded extremity of the tail, then forms a slightly curved 

 bow, and the course through which it passes follows a similar 

 curve. When the membrane, and with it the head, are quiescent, 

 the tail is seen slosvly bending and twisting about, although 

 without producing any perceptible change of place. 



Deceived by such manifold movements, I was led, in 1860, to 

 regard these structures as parasitic animals, in which, however, 

 I vainly endeavoured to discover traces of a mouth, intestine, &c. 

 But when I was recently (18G2) again able to examine a male 

 lanthina, I found my supposed parasites so densely packed in 

 its semen, that I began to doubt whether I had not before me 

 an essential constituent of the semen. And then I was at once 

 struck with the similarity between the agitated hairs of the tail 

 and seminal filaments which have nearly attained maturity, but 

 have not yet separated from the place of their formation ; and I 

 soon succeeded in breaking up several tails into groups of un- 

 mistakeable seminal filaments, perfectly resembling those which 

 were swimming about freely in the seminal fluid. 



That these structures are an essential constituent of the semen 

 was consequently established. But are they the formative organs 

 of the seminal filaments, from which these subsequently, when 

 mature, separate ? or are they " spermatophora,^' around which 

 the mature seminal filaments have collected ? The former notion 

 appears to me the more probable one ; it is supported especially 

 by specimens frequently observed, in which the seminal filaments 

 were not only motionless, but also appeared to be shorter than 

 in the others. Besides these, numerous other still younger forms 

 were seen : the youngest that came under observation was of the 

 form of an elongated e^^, about 0*2 millim. in length and 

 0*1 millim. iu breadth. The greater part of this oval body ap- 

 peared perfectly transparent and empty ; the thickened end alone 

 was occupied by a roundish mass, which was rendered opaque by 

 densely imbedded granules. It appeared darker on the side 

 turned towards the apex of the egg, and lighter on the opposite 

 side, although no distinct line of demarcation could be detected 



