38 Moll 
MOLLUSCA. 
Limncea. According to the structure of the tail two groups may be 
made :—(1) In Succinea, Ccirocolla, Helix, the head has a twisted structure, 
consisting of two precisely similar threads; in the tail a third one is 
coiled round them. (2) The third thread is absent both in head and 
tail ; the extreme tip of the latter consists only of one thread. Every¬ 
where in the hinder two-thirds of the head is a strongly refracting central 
streak, and the tail has a spiral axial thread. The movement of the 
spermatozoon is an intermittent rotation about the axis, and cannot be 
attributed to a flagellate motion of the tail, which goes first. 
Spermatogenesis in the Pulmonata has been observed by Platner 
(291a), who finds that at an early stage the spermatogonia and the ova 
are the only kinds of cells in the hermaphrodite gland ; each of the for¬ 
mer contains, in addition to the nucleus, a peculiar structure, consisting 
in A rion of an angular figure composed of rods, and in Helix of a coiled 
filament. Some spermatogonia form spermatocytes, but others persist, 
arranged in columns which arise from the alveolar wall, between the 
groups of spermatocytes. Spermatides are the final product of the divi¬ 
sion of the spermatocytes ; they have a large granular nucleus, and show 
amceboid movements; from the protoplasm a process juts out, which 
increases in length, and is called the “ primary spermatic filament,” or 
extracellular portion of the spermatozoon. The nucleus becomes formed 
afresh, and by a peculiar invagination forms the intracellular portion of 
the future head, and unites with the primary filament. Some critical 
remarks are appended, showing the theoretical bearing of the observa¬ 
tions. 
Spermatozoa of Anodonta cellensis and Paludina vivipara (as well as 
other structures) figured by Carnoy (Cellule) to show the disposition 
of the nucleus, which vanishes in the latter species during development. 
Sabatier (318) describes the formation of the egg-membranes of Chiton , 
and obtains results agreeing with those of Fol and others in the Tuni- 
cates ; he also remarks on the disposition of the germinal vesicle. The 
same author (318a) has also observed that in Buccinum and Limncea 
globules are extruded from the ova at various positions on their surface ; 
for instance, opposite the point at which the polar cells appear ; these 
globules may multiply by division outside the ovum. 
Viable ton (370) finds that on the ventral lobe of the buccal mem¬ 
brane, where spermatophores are attached, there are found pit-like glands 
(poches copulatrices). In Loligo these glands are united into a single 
mass, opening in the middle line, and the author has seen females hold 
their eggs between their ventral arms, and supposes that they are then 
fertilized before they receive their protective covering. 
Patten (283) has artificially fertilized Haliotis and Patella. 
Egg-capsules of Fulgur in process of development observed by Ford 
(132). Fulgur perversus has been observed to descend into the sand 
preparatory to laying its eggs; it affixes the case to a shell, and then 
ascends till it can respire freely ; in this position it completes the opera¬ 
tion : Willcox (378). 
Oviposition observed in Parmacella valenciennesi , Webb & V. Ben.; 
Crosse (89). 
