42 SUMMARY OF CURRENT RESEARCHES RELATING TO 



posed, ncrvc-fibrcs, but nitatcrials which serve to make ui) the limiting 

 fibres. 



The author regards as one of his most striking results the know- 

 ledge of the mode of formation of the rhabdome — a structure which is 

 so characteristic of the Arthropod eye. The difference in the mode of 

 formation must cleai'ly have some influence on the process of per- 

 ception, into the consideration of which Grenacher enters. 



Histology of Pteropods and Heteropods.*— Dr. J. Paneth deals 

 chiefly xs'ith the " foot " of Ptcrotrachea, Cymbulia, and Tiedemannia. 



The external investment is a unilaminar pavement — epithelium, 

 except on the borders of the " foot " and in certain other regions, 

 where it consists of a cubical or cylindrical ciliated epithelium which 

 Dr. Paneth terms a sense-organ because of its rich nerve-sujjply and 

 tactile hairs. Epithelial in nature arc certain papillae on the foot 

 in Ptcrotrachea, which are apparently sensory in function. The 

 " cartilage," underlying the epithelium of the foot, contains (1) in 

 Heteropoda, "stellate cells"; (2) in Pteropoda, "fibrillar cells." 

 Amoeboid cells occur in both classes with these characteristic 

 elements. Gegenbaur would appear to be wrong in saying that 

 Pteropoda do not possess " cartilage." 



The muscles of both classes consist of bundles of cells resembling 

 the involuntary muscles of Vertebrata. The cells are spindle-shaped, 

 with a long nucleus, with homogeneous protoplasm. There are traces 

 of transverse striation. 



Both in Heteropoda and in Pteropoda the peripheral nerves show 

 a distinct fibrillar structure, the finer nerves showing a homogeneous 

 character. Aggregations of protoplasm occur at the points of nerve- 

 division and where trunks cross one another. A nucleus is generally 

 found in these protoplasmic masses, which have been by some thought 

 to be ganglionic in nature. Dr. Paneth has never seen any relation 

 between them and the nerves that pass near them. 



The nerves end (1) in the cartilage (corresponding to the con- 

 nective tissue of higher animals) by a ramifying terminal network of 

 " primitive fibrils," which do not enter into any union with other 

 histological elements ; and (2) in muscles by means of a rete, the 

 fibrils of which reunite to form a trunk which issues from the muscle 

 much as it entered. A Doyerian eminence marks the entrance of the 

 nerve. 



Generative and Urinary Ducts in some Chitons. f — Prof. A. C. 

 Haddon describes the generative and urinary ducts in some Chitons, 

 in which he shows that the previous investigations on the presence or 

 absence of genital ducts in this group are not to be accepted without 

 verification. The posterior fenestrated area on the under surface of 

 the mantle is in reality glandular, and it is suggested that they may 

 be the homologues of the caocal glands described by Hubrecht in 

 Proneomenia. 



* Arch. f. Mikr. Anat., xxiv. (1884) pp. 230-88 (3 pis.). 

 t Sci. Proc. R. Dublin Soc, iv. (1884) p. 223. 



