DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 693 



may enter in this form (No. 89). In osseous fishes a similar condition would appear to 

 obtain, one spermatozoon being sufficient ; but as this does not plug up the micropyle, 

 others may also enter, indeed, Ransom observed this in Gastrosteus. " I watched closely 

 one egg," he says, " which was placed with the micropyle in full face, so that the aperture 

 at its apex was well seen. Spermatozoa approached and entered the funnel, and 

 one was watched till it disappeared, apparently in the direction of the interior of the 

 egg, just at the moment when it seemed to occupy the aperture at the apex of the 

 micropyle. Immediately after the depth of the funnel began to diminish, and a 

 breathing chamber commenced to form ; two or three more spermatozoa were, less 

 distinctly, seen playing about in the apex of the funnel as it was shortening ; one of 

 them appeared to become still before it vanished apparently inwards" (No. 127, p. 461). 

 The exaggerated length of the micropylar funnel, which Ransom describes in Gastrosteus 

 as enabling it to dip into the granular discus proligerus, has not been described in other 

 Teleosteans, Neither Andre nor Gerbe mention it in the trout, nor does His show it 

 in the trout or salmon; while in pelagic eggs the micropylar eminence, though distinct, 

 is not by any means prominent (PI. I. figs. 11-14). A lengthened micropyle is indeed 

 unnecessary, the mere presence of the spermatozoon within the ovum being the 

 essential point. The actual entrance of sperms has been seen in very few Tele- 

 osteans. Ransom, as already noted, saw them occupying the external orifice of the 

 micropyle, and Andre speaks of observing a sperm apparently entangled, in the micro- 

 pylar canal, by the jutting ends of the radial striae, which appeared to him to serve 

 for securing the sperm after its entrance (No. 4, p. 201); but there seems to be no 

 column of protoplasm facilitating the passage of the sperm from the micropyle to the 

 female pronucleus, such as Calberla describes in Petromyzon planeri. The head of 

 the sperm in this form separates from its flagellum, and passes along the proto- 

 plasmic column, which withdraws from the micropyle (Calberla's aussere Mikropyle), 

 and the sperm proceeds through the neck of the column (distinguished as the inner 

 micropyle) to the enlarged central termination, where the " eikern " or female pro- 

 nucleus is seated. Here conjugation of the two pronuclei is effected (No. 38, p. 458, 

 Taf. xvii. figs. 5, 6, 7, and 8). Possibly the preformed discus proligerus may repre- 

 sent this column ; and in those Teleosteans in which no disc is formed, the distance 

 between the inner orifice of the micropyle and the protoplasmic cortex of the vitellus 

 is insignificant. The spermatozoa of Teleosteans seem to be of the ordinary type, 

 and show, so far as observations go, little difference in structure — the usual head 

 or enlarged portion being distinguishable from the hair-like tail or flagellum (PI. I. 

 fig. 9). 



Polar Globules. — The details of the phenomena of fertilisation in osseous fishes are 

 probably not unlike those in forms more fully known. Hoffman has described the 

 formation of the pronucleus and ejection of a polar globule in Scorpcena, Julis, and 

 Crenilabrus, and he states that the globule closes up the orifice of the micropyle, 

 and prevents the admission of other sperms after that of the single sperm which 



