Mr. H. J. Carter on Microscopic Filaridse. 39 



tophorous ones ; but here, in Urolabes palustris, while the deve- 

 lopment still goes on within the parent cell, and the spermato- 

 phorous cells adhere to its internal periphery, in Nais fusca the 

 parent cell is lost, and the spermatophorous vesicles become 

 fixed to a central albuminous mass until the spermatozoa are 

 developed*. 



The fact of the granules (which become the vesicles or daugh- 

 ter cells) being within the spermatic cells here, as well as in 

 Nais fusca f, makes me doubt the interpretation which Dr. Nel- 

 son has given to their appearance in the testicle-sac of Ascaris 

 mystax, where he states that the spermatic cells are met in their 

 progress downwards through the testicular sac by a number of 

 granules " which group themselves around^' them, and continue 

 about them until they get into the '* uterus" of the female, 

 where they drop off and form a '' granular fluid,'^ leaving the 

 spermatic cells naked J. As, however, my observations are 

 based upon Dr. Nelson's statements, and not on actual examina- 

 tion of A. mystax, I will merely add, that the grouping of gra- 

 nules around the spermatic cell appears to me to be a phseno- 

 menon as inexplicable as it is anomalous. 



That the spermatic cells themselves should be thrown off the 

 inner surface of the testicular tube of A. mystax in " granules," 

 I can easily conceive; but the impossibility of getting at the 

 inner part of the end of the testicular tube in Urolabes palustris, 

 left to the mere chance of the position it may take after bursting 

 through the integument from pressure, and by moving the 

 covering- slip of glass (for these parts are far too minute to be 

 otherwise manipulated), is such, and the rapid imbibition of water 

 by the cells situated there so distends the contents at the end of 

 the tube, that it is impossible to ascertain anything satisfactorily 

 beyond the fact that it does contain cells, and that these cells 

 produce the spermatozoa. By a " granule" which passes into a 

 nucleated cell here, I do not understand a simple aggregation 

 of matter, but a point of complicated structure which we call a 

 granule because its structure is too minute for us to demonstrate 

 by the microscope. 



Impregnation. — This appears to take place at the moment 

 when the ovum reaches the mouth of the fallopian tube (13/), 

 and to require that the spermatozoon shall have left its cell 

 before the incorporation can be accomplished, — 1st, because the 

 germinal vesicle and its nucleus appear full and prominent in the 

 ovisac at this point, and disappear rapidly after the ovum has 

 passed into the fallopian tube ; 2ndly, because up to this time 

 the ovum is without the coriaceous coat with which it afterwards 



* Annals, vol. ii. pi. 3. t Id- pl- 2. fig. 5. 



J Phil. Trans, p. 505, &c., 1852. 



