734 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The lining of the peritoneum is a thin layer of largo very flat cells, 

 of which, in section, one can generally distinguish only the nuclei, which 

 are placed at some distance from one another. The coelom is only 

 incompletely separated into segments by dissepiments, as the cavities, 

 especially around the ventral medulla, are in communication with ono 

 another. ' The dorsal mesentery of Criodrilus appears to be aborted. The 

 surface of the intestine and of the dorsal vessel is invested by a layer of 

 much modified peritoneum — the chloragogue-glands. These are pyriform 

 or saccular cells, with brown, coarsely granular contents, which, as a 

 rule, hide the nucleus. The muscles of the dissepiments and of the 

 coelom extend in very various directions. 



On the whole, the author confirms the description given by Vejdovsky 

 of the structure and arrangement of the nervous system, but he was not 

 able to detect the well-developed layer of cells which that author 

 describes as lying on the ventral half of the ventral medulla ; he finds, 

 indeed, that the ganglionic cells are arranged in four rows ; the whole of 

 the median part of the cord is occupied by fibrous substance in which 

 tracts, which follow various directions, can be made out. The walls of 

 the large neural canals appear to have double contours. In the hinder 

 part of the body there are two, but in the median part three canals, so 

 that Vejdovsky's figure represents a section of the hinder part of the 

 body. The median canal is at first of the same size as the two lateral, 

 but in the median and anterior part of the body it has a considerably 

 greater diameter. In some of his sections the author was astonished to 

 find a fourth canal underlying the median third, with which at one point 

 it was observed to become connected. 



Around the tip of the tail there are groups of hairs, which are much 

 longer than the setfe of the gustatory knobs. As it was often observed 

 that worms which had extended the caudal portion for the purpose of 

 breathing were very sensitive to sudden movements of the water, it may 

 be supposed that these hairs are special tactile organs for the perception 

 of movements of the water. 



Like the Lumbricidae, but unlike the Limicolas, Criodrilus has a 

 longitudinal subneural, as well as a dorsal and ventral vessel. In 

 segments seven to eleven the lateral vessels take on the function of a 

 heart. In the dorsal vessel there are valves, which are arranged in a 

 segmental manner; the author does not agree with Kuppfer in re- 

 garding them as blood-forming organs, but as true valves which, on the 

 contraction of the vessels, shut otf two adjoining chambers from one 

 another, and prevent the return of the blood. In addition to the super- 

 ficial capillaries at the hinder end of the body, it was observed that 

 there is a large collection of capillaries in the hypodermis of the cei^halic 

 region, by means of which a good supply of oxygen is obtained for the 

 brain. 



Segmental organs are present in the generative segments, and this 

 points to close relations between Criodrilus and the Lumbricidfe. The 

 pharyngeal mass, which can be protruded, is provided with three strong 

 groups of retractor muscles, but with only one protractor. The author 

 agrees with Eosa and Benham in asserting the presence of a typhlosole, 

 •which was stated by Vejdovsky to be absent. In most points he agrees 

 with the descriptions of the generative organs which have been recently 

 given by Eosa, Oerley, and Benham. 



In a few cases, but then in large number, the ccelom, and especially 



