40 Moll. 
MOLLUSCA. 
Two modes of development of spermatozoa are described in Aplysia 
but there does not appear to be any morphological difference between 
them ; Robert. 
In Murex the nuclei which give rise to the spermatogonia are disposed 
as in Avion and Helix , and give rise to two different kiuds of elements : 
voluminous cells, which are the mother cells of the vermiform sperma- 
tozoids, and small membrane-less cells, which are the mother cells of the 
filiform spermatozoids. These are quite distinct throughout their whole 
existence. The differences which obtain in the cases of If. brandaris and 
M. trunculus are noted. The vermiform spermatozoa are morphologically 
ova, and seem to have no determinate function. Perhaps they represent 
in the testes of the higher Prosobranchs the ova of the hermaphrodite 
gland of the more archaic Prosobranchs ( Monotocardia ) ; Kcehler. 
Observations upon the mother-cells (spermatogonia and spermatocytes), 
at rest and in division, and upon the spermatic cells and their differentia- 
tion into spermatozoids, lead to conclusions at variance, in many respects, 
with those of Platner • Prenant. 
In the Chitonidce only one membrane ever encloses the egg ; it may be 
termed “ follicular,” and is always composed of nucleated cells, sister cells 
of the ovum ; the structure of the mature egg is described, and the 
expansion and contraction of the vitelline masses ; Garnaolt (2) 
The oogenesis and fertilization of Helix and Avion treated histolo- 
gically ; id. (3, 5, 9). 
Experimental proof that hermaphrodite Snails are self-fertilising ; 
Braun (2, 5). 
Helices , when once impregnated, can lay eggs several years without 
further coitus ; oviposition takes place from May to July ; Brock- 
meier. Further observation on Helices j Hartwig. 
Copulation and oviposition of Eledone and Sepia described j Joubin (1). 
The spermatophores in the female Uossia oweni were found embedded 
in the skin below the eye ; Hoyle (1). 
Statements as to the time of sexual maturity of various species; 
Lo Bianco. 
Hectocotylisation of Inioteuthis , spp,, described ; Ortmann, p. 647. 
Right tentacle enlarged and curved outwards in male of Campeloma ; 
Call (2). 
Sucker in female of Pterotrachea ; Fewkes (2). 
Those so-called females of Pterotrachea which have suckers are pro- 
bably males which have lost the penis by the attacks of Crustacea ; 
Giard (3). 
List of Mollusca in which parasitic castration has been observed; id. ( 1 ). 
Castration of Helix aspersa by the sporocysts of a Trematode ; Gar- 
NAULT (7). 
Nidus of Lunatia heros ; Seidensticker. 
Ova have been found to be nursed in the gill-chambers of Unio , Sipho- 
naria, Patella , and Acmcea ; Ten ISON- Woods (1). 
Egg masses on the shell of Hydrobia ulvce , probably its own ; Herdman. 
For a few remarks on records of hybridity, see Suciietet, 
