Reproductive Structures in Chaetognaths — Alvarino 
489 
In un solo esemplare la spermatofore era intera ; 
in altri, invece, soltando la membranella lacerata 
sporgeva dagli orifice genitali. Nessuno degli 
esemplari esaminati ha purtropo le vescicole 
seminali mature a cio impossibile ogni supposi- 
zione sul come si formino le spermatofore.” 
It is unfortunate that neither David (1958) 
nor Ghirardelli (1959^) studied the structure of 
these sacs or their contents to ensure identifica- 
tion. Ghirardelli (1959^), commenting on the 
sac with mature eggs in Eukrohnia, stated, "le 
poche ouva devono essere fornite di notevolu 
quantita di materiali di reserva ed in oltre pro- 
tette nella particolare tasca incubatrice.” 
Alvarino (1962), when first describing E. 
bathypelagica, stated, "the fins are broadest at 
the tail region, where they bend to the dorsal 
side. . . . This phenomenon is incipient in E. 
hamata and E. fowler/, but in E. bathypelagica 
is more conspicuous, as this part of the fin is 
broader.” The species of Eukrohnia studied by 
Alvarino in 1962 did not include E. bathyant- 
arctica. She also stated for E. bathypelagica, 
"The laminar part of the lateral fins bends to 
the dorsal side, which helps drive the sperma- 
tozoa into the oviducts, and probably also bears 
the newly hatched eggs.” 
Schilp (1941) referring to E. hamata ob- 
served, "The ovaries project outside the body. 
The cause of this abnormality is unknown to 
me.” The iridescent membranous funnels at the 
openings of the oviducts which he mentioned 
for E. richardi Germain and Joubin (probably 
E. foivleri ) might be remnants of the incubatory 
sacs. 
Alvarino (1967, 1968) illustrated some pieces 
of a saclike remnant hanging from the oviduct 
of E. fowleri. Dawson (personal communica- 
tion) observed a marsupial sac filled with eggs 
hanging from the oviducts of specimens of E. 
bathypelagica collected at the ice-cap region of 
the Arctic. 
Personal observations on specimens of E. 
bathyantarctica from the antarctic and suban- 
tarctic regions, collected recently by the R. V. 
"Eltanin” during the United States Antarctic 
Research Program (U.S.A.R.P.), detected the 
sac containing eggs protruding from the open- 
ing of the oviducts. The brood sac (marsupial 
sac or brooding pouch) appeared of different 
sizes in various specimens, indicating various 
stages of development. The mature eggs in this 
marsupial sac were observed at different stages 
of development, from the formation of the 
blastomeres to the various phases of develop- 
ment of the embryos, up to the larval stage 
ready for eclosion. Some specimens showed 
remnants of the sac hanging from the oviducts. 
Those specimens presented one sac at each side, 
and the widest part of the lateral fins was bent 
dorsally covering more or less completely the 
marsupial sacs. 
The brooding phases could be outlined as 
follows: Stage I, brood sac developing (Fig. 
1 A) ; Stage II, brood sac filled with mature 
eggs, up to gastrula; Stage III, brood sac with 
eggs containing embryos in a single coil (Fig. 
I B) ; Stage IV, brood sac with eggs containing 
double coiled embryos ; Stage V, brood sac 
broken after the eclosion of the larvae (Fig. 
IC) . 
The illustrations were obtained using the 
stereomicroscope with the drawing tube attach- 
ment. 
In the illustrations (Fig. 1) the seminal 
vesicles are clearly visible, evidence that David’s 
observation (1958) that "the 'ruptured sacs’ 
attached to the oviduct were seminal vesicles,” 
was an erroneous assumption. 
Tokioka (1939), when describing Bathyspa- 
della edentata , indicated the presence of a "cap- 
sula-like opening at the seminal receptacle” — 
a small bag at the opening of the oviducts. This 
might have been related to the brood sacs be- 
ginning to develop. 
Ritter-Zahony (1910) explained that in the 
genus Krohnitta brooding sacs are not present. 
However, Schilp (1941) noticed small mem- 
branous sacs at level with the trunk-tail septum 
in K. subtilis (Grassi). 
Sanzo (1937) observed the pelagic ootheca of 
Pterosagitta draco (Krohn) containing mature 
eggs. The gelatinous substance of the ootheca 
protects both the eggs and larvae from the vari- 
ous physico-chemical changes until eclosion. In 
the Straits of Messina, this author found gelatin- 
ous colonies 6.0 to 6.4 mm in diameter, with 
spherical transparent eggs 0.3 to 0.4 mm in 
diameter. 
Hertwig (1880) observed free deposition of 
eggs in Sagitta bipunctata Quoy and Gaimard 
and in S. serratodentata Krohn. 
