244 SUMMARY OF CURRENT RESEARCHES RELATING TO 



in the changes which various parts have undergone, the nervous 

 system has not remained fixed; it has followed the cloaca and 

 mesenteiy, and particularly the cement-glands; in such a position 

 also we must look for the nervous system of other Centrogonida, 

 until and unless we find a type in which the cement-glands have 

 become widely separated from the mesentery and the cloaca ; in such 

 a case it will be interesting to discover what the nervous system has 

 done. 



Vermes. 



Dorsal Pores of Terricolous Oligochseta.*— Herr H. Tide in- 

 vestigated the pores and the histology of the dermo-muscular tube of 

 earthworms by the method of sections ; the worms were killed in 

 dilute (1/2 per cent.) chromic acid, and hardened for eight to ten 

 hours, washed in water, and placed in 70 per cent, alcohol ; Hamann's 

 neutral acetic acid carmine was used as a colouring agent. This 

 method destroys the longitudinal muscles, the relations of which 

 must be studied by killing in boiling water, hardening in a mixture 

 of one part concentrated picro-sulphuric acid and three parts distilled 

 water, then extended on a cork for eight hours. Grenacher's borax- 

 carmine may be used as the staining agent. If the animals are to be 

 preserved in absolute alcohol, they must be stupefied by chloroform 

 vapour. 



The diameter of the pores varies from 1/100 to 1/106 of the 

 circumference of the body in the six species examined; the pore 

 appears to increase with the growth of the body ; as a rule, to which 

 Allolohophora mucosa is an exception, the pores disappear in the 

 clitellar segments, when the clitellum becomes developed. The 

 muscular fibres of the circular layer form a special complex around 

 the pores, and appear to have the function of closing them ; the 

 longitudinal muscles, on the other hand, seem to have a duty in 

 relation to opening the pores. The author gives a detailed account 

 of the histology of the dermo-muscular tube, and enters into a close 

 comparison of his results with those of other observers. 



Notwithstanding the abortive results of his predecessors, the author 

 thinks he is able to show that the dorsal pores have a definite arrange- 

 ment ; the first pore may, when a number of species are compared, be 

 found to be pushed back gradually from the fourth to the thirteenth 

 intersegmental groove ; and the species may be arranged in groups in 

 which the first pore has a constant position, and this may be regarded 

 as an indication of affinity. The existence of a peritoneal coelom is 

 necessary for the presence of dorsal pores, but, on the other hand, 

 there are tracts of the body which possess this coelom but no pores ; 

 there does not seem to be any relation between the pores and the 

 nephridia. It is doubtful whether the pores are really absent from 

 such terricolous Oligoch^tes as have been said to be without them ; 

 but they seem to be always wanting in the Limicolse. 



At certain times, and under certain conditions, the perivisceral 

 fluid and its elements may be passed out by the pores, which, there- 



* Zeitscbr. f. Wiss. Zool., xliii. (1885) pp. 87-143 (1 pi.). 



