ON THE ANATOMY OF SAGITTA. 193 
with spermatic elements; the peculiar spermatophores were 
already fully formed, and the ovaries were so much developed 
as to be readily forced by pressure into the head. It would 
seem, therefore, that the species is one of the smallest known. 
The principal peculiarity which especially induced Dr. Pa- 
genstecher to direct attention to the form, consisted in the 
existence of a pair of special organs on the dorsal aspect of 
the head, one on either side. ‘These organs were placed at 
the base of the upper lip, in front of the lateral bundles of 
sete, externally and in front of the eyes. The organ itself 
consisted of a minute tube or saceulus, imbedded in the 
integument; the walls of the sacculus were coloured with 
opaque, brown, and inky pigment-molecules. It appears 
that these follicles opened on the sides of the head with a 
minute orifice, surrounded by a firm, strongly refracting 
border. Are these organs to be regarded as olfactory, or as 
analogous with the glandular follicles which are found in the 
cervical region in the Nematoda? 
Leuckart and the author, in their common researches on 
the lower animals (of Heligoland), have shown that in Sa- 
giita germanica the intestine is attached, not only by mesen- 
teries, but also, as in the Nematoda, by a network of flattened 
bands, and, consequently, that there can be no question of 
the existence of a true perivisceral cavity. 
In Sagitia gallica the most anterior border of the peri- 
visceral space within which the intestine moves about freely 
during the movements of the hook-dise, and at which border 
these peculiar fixing bands are not seen, is distinguished by 
the presence of a complete transverse circlet of delicate, 
yellowish, oval cells, applied to each other by their lesser 
diameter. The intestine passes backwards through this ring, 
and by pressure the ceca! end of the ovaries can be forced 
in the opposite direction, towards the head. Externally to 
this is the sac formed by the obliquely and intricately inter- 
laced muscular fibrils. From this arrangement it follows 
that the anterior portion of the intestine possesses great free- 
dom of motion, in consequence of which the movements of 
the oral disc and pharynx are much facilitated. The orga- 
nization of the border of the upper lip, the circle of large 
cells around the mouth, and many other peculiarities of struc- 
ture belonging to the genus Sagitta, were also observed in 
this species. It is not impossible that Busch saw and figured 
the above-described organs in Sagitta, but he explained 
them as being retractile and protrusile tentacles, of which, 
however, Dr. Pagenstecher has been unable to perceive any 
yestige, é‘ 
