72S 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
The student is warned that those who try to find a complete cycle of 
metamorphoses in their own special lines of research will often be 
disappointed, and probably question whether it exists at all. 
B. INVERTEBRATA. 
Mollusca. 
Lingual Cartilages of Mollusca.* — Dr. G. Loisel divides the 
lingual cartilages of Mollusca into two great groups ; in many 
(Pulmonate Gastropods, certain Nudibranchs, Cephalopoda) they are 
formed of muscular fibres, among which are connective elements as in 
other muscles ; here, because of the function which the organs have to 
fulfil, the connective cells almost always become vesicular. In other 
Mollusca (e.g. Buccinum) the lingual cartilages are formed of true 
cartilage-cells without any admixture of muscular fibres. Intermediate 
stages will probably be found between these two classes. 
The word cartilage ought not to be employed to distinguish the 
organs that support the radula, and it would be better to speak of 
supporting pieces. The papilla or formative sheath of the radula may 
contain connective tissue in a mucous or gelatinous form. 
The smooth muscular fibres of Gastropods are formed of two sub- 
stances ; one is fibrillar, and represents the contractile element, the other 
is granular and protoplasmic ; but the topical relations of these are not 
constant, as is generally asserted. In following the development of a 
smooth fibre it may be seen that the differentiation of the protoplasm 
into fibrils goes on from the periphery towards the centre ; when the 
fibre has reached its maximum development the nucleus of the primitive 
cell seems to have completely disappeared. The smooth muscular 
fibres found in the supporting pieces of the radula differ from ordinary 
fibres by their greater breadth, and by the difference in their reaction 
to staining agents. Transversely striated muscular fibres, similar to 
those of Insects and Vertebrates, are sometimes found in the lingual 
muscles. There is very little connective tissue in the muscles of 
Gastropods ; it is most often merely represented by some fine granula- 
tions and by nuclei. At a certain stage in their development the 
muscles of Gastropods have large vesicular cells among their fibres. In 
many muscles these cells disappear in the adult stage, but when the 
function of the muscle requires it they may persist : this happens, for 
example, in the supporting pieces of the radula. 
The form of the cartilaginous tissue has a relation to the connective 
tissue of the same animal ; that found j in Buccinum gives gelatin on 
boiling, and is stained yellow by iodine, and bright rose by picro- 
carmine. The cartilage with branched cells which is found in Cephalo- 
pods is a primitive form which is directly related to the connective 
tissue. 
Nervous System of Lamellibranchs and Gastropods.! — M. A. 
d’Hardiviller brings forward evidence to show that there is no difference 
between the central nervous system of Lamellibranchs and that of Gas- 
tropods. The stomato-gastric system, the pleural ganglion aud the 
* Joum. Anat. et Physiol., xxix. (1893) pp. 466-522 (28 figs.), 
t Comptes Bendas, cxvii. (1893) pp. 250-2. 
