308' Prof. H. Karsten on Rhynchoprlon penetrans, 



unimpregnated animal (PL VIII. fig. 5), and in the outer per- 

 gamentaceous capsule of which there is at each end a group of 

 small pores (the so-called micropyles), lie in the part of the ovary 

 nearest to the vagina (PI. VIII. fig. 12 v), and close to its 

 eff"erent duct (fig. 12 w), without exhibiting the least sign of 

 fecundation. 



This efferent duct, which is common to the two ovarian tubes, 

 opens into the fecundation- sac (fig. 12 Z*), formed of a delicate 

 elastic membrane, into which the long afferent canal from the 

 large seminal receptacle opens; the latter is filled with long 

 filiform spermatozoids, which are not free in this receptacle, but 

 each of them is rolled up singly in a spiral, and cemented into 

 a small ellipsoidal corpuscle by a substance which is soluble in 

 water. The pyriform seminal receptacle is composed of an elastic 

 tissue, and is coated externally with striated muscular fibres and 

 cellular tissue. If the seminal receptacle, taken from a recently 

 killed animal, be torn under water, the small ellipsoidal sperma- 

 tophores (fig. 10) with which it is filled break up, and from 

 each of them is evolved a long seminal filament (fig. 11), which 

 moves for some time in water. 



It was found impossible to observe a mature ovum in the 

 fecundation-sac ; for, as soon as the operation of extracting a 

 pregnant female from the skin is commenced, a large g,^^ is 

 usually projected from the cloaca, no doubt in consequence of 

 the pressure exerted upon the insect. The fecundation-sac is 

 therefore always found empty and collapsed (as here figured). 



The natural process, in my opinion, is as follows : — The ripest 

 ovum, impelled into the fecundation-sac by the pressure of the 

 increasing ova behind it, meets there with some spermatozoids, 

 which have previously been set free and migrated from the 

 seminal receptacle; these fecundate it, excite in it the process 

 of cell-formation, and induce the development of the embryo. 

 In consequence of these processes, the egg begins to enlarge and 

 to expand the elastic fecundation-sac, and it is finally expelled 

 "through the vagina in consequence of the pressure applied to it 

 by the sac. 



If the development of the larva in the one fecundated ^^^ 

 took place in the fecundation-sac or the oviduct, there would 

 always, as in the PupiparOj be only one larva in the parasite; 

 but the penetration of this larva into the nutritive body, asso- 

 ciated as it would be with perforation of the walls of the mother, 

 would prevent the natural development of all the other ova. 

 For the position of the cloaca in the orifice of the epidermis 

 produced by the penetration of the parasite, and immediately 

 . at the surface, would render it necessary, in order that the ex- 

 ^jluded larva might reach the mucous membrane, that it should 



