752 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Beneath the epidermis there is one very thin muscular layer, which consists 

 merely of the primitive longitudinal fibres which stretch uninterruptedly 

 from head to tail. The segmentation of the alimentary canal appears to be 

 independent of that of the body generally. With regard to the limitation 

 of the " segmental organs " to the head, it is of interest to be reminded that 

 a similar condition obtains in the larva of Polygordius. 



The entire length of the nervous system lies in the epidermis. It con- 

 sists of a cerebral ganglion and two commissures, which pass to the ventral 

 surface, where they unite to form the nerve-cord ; as in Halicryptus and 

 Priapulus epithelial and ganglionic cells seem to merge into one another. 

 No peripheral nerves were seen ; the only sensory organs are two small 

 ciliated pits, one on either side of the cerebral gaDglion. No traces of 

 reproductive organs could be found, but there is fissiparous reproduction, 

 similar in character to that described by Kennel for C. pardalis. As in 

 it, almost every segment becomes a zooid, which rapidly developes into the 

 multi segmented form ; a bud appears between two segments, and the buds 

 are produced in the same order as new segments, i. e. from before backwards. 

 As is well known, in Naids, the buds appear in the opposite order, and on 

 this Semper's " proglottidentheorie " is based ; but it is clear that it will 

 not apply to Gtenodrilus ; differentiation of the budding zones, unlike, again, 

 what happens in Naids, does not go far until division of the animal. In all 

 observed cases the act of fissiparous reproduction of C. parvulus was com- 

 pleted within forty-eight hours. 0. monostylos differs in that there is no 

 appearance -of buds, the animal merely breaking up into two almost equal 

 parts, each of which may again divide into two or more parts. 



Natural History of the G-enus Dero.* — Mr. E. C. Bousfield gives a 

 history and bibliography of this genus, with notes on their habits and the 

 nature of their tubes, with some hints as to the methods of observation. A 

 description of the general character is succeeded by a more detailed account 

 of the branchial apparatus. 



The author regards the " segmental organ " as purely mechanical in 

 function, in " preventing undue distension of the body by the fluid which 

 passes through the walls of the intestine, and is doubtless charged with effete 

 material from the blood-vessels which run in contact with it." Moreover, 

 what is generally considered to be the movement of cilia in these organs he 

 maintains to be due to the vibration of a membrane, the free edge of which 

 can be seen when vitality is at a low ebb. Observations on Tubifex, Nais, 

 Stylaria, and ^losoma lead him to this view. The sessile habits of Dero 

 necessitate some greater opportunity for oxidation of the blood than is 

 provided in other worms by the current of water which is continually flow- 

 ing in at the anus. The form of the branchial area varies in the different 

 species, but there are never more than foir branchial processes. 



A systematic description is given of the asexual forms of the seven known 

 species. 



Histology of the Integument and Sensory Appendages of Hermione 

 hystrix and Polynoe Grubiana.f — M, C. Jourdan gives an account of the 

 dorsal cirri of Hermione hystrix, which seems to show that these organs are 

 tactile. Owing to the movements of the parapodia with which they are 

 connected they are able to exercise true tactile functions. The nerve which 

 passes to them enters into communication with the exterior at the level of 

 the pores, and there is a richness of innervation and a frequency of connec- 

 tion with the epithelial elements which shows well the specially sensory 



* Journ. Linn. Soc. Lend , xs. (1887) pp. 91-106 (3 pis.), 

 t Arch. Zool. Exper. et Gen., v. (1887) pp. 91-122 (2 pis.). 



