446 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Lumhricus olidus Dr. Kohde observed the occurrence alsb of ccelo- 

 myary forms. 



Phreoryctes most closely resembles BrancMohdella. All the otlier 

 Chsetopods exhibit a decidedly weaker development of muscle-cells, 

 and much less medullary substance. In Limicolse the usually flat 

 muscle-cells form a single row ; in the Lumbrici this is folded so 

 that bundles are formed ; in Criodrilus these groups of cells are 

 replaced by an entirely irregular disposition. In Serpula and Proiula 

 among Chjetopods, highly complicated forms of bundles occur; in 

 Spirographis hints of bimdles occur only here and there; in the 

 other Polychaetes the cells are disposed either in strands (Arenicola, 

 Terebella), or in small groups (Polynoe, Eunice, Chsetopterus), or quite 

 irregularly (AmmocJiares, Nephthys). The cells themselves are on an 

 average much smaller than those of Oligochsetes, but the longitudinal 

 layer, as a whole, is more strongly developed. 



Between the muscle-cells, and frequently between them and the 

 body-cavity, a nucleated mass occurs, often closely apposed to the 

 surface of the cells. This Dr. Rohde regards as the formative sub- 

 stance of the musculature. Eound the cells there is always a fibrous 

 intermediate tissue, not, however, a proper connective tissue, but rather 

 a secondary separated product of the muscle-cells. 



The contractile cortical substance of the cells is resolved into 

 primitive fibrils arranged radially in fibrillar plates which pursue 

 a spiral course round the fibres. In this radial disposition of the 

 primitive fibrils the Chsetopods resemble the Nsematodes, Hirudinea, 

 and partly the Gephyrea. A transverse striation is often recognizable, 

 due to the interrupted swelling of the muscle-cells. A great tendency 

 to longitudinal splitting is very evident. 



The memoir closes with an interesting comparison of the Chsetopod 

 musculature with that of the Platyhelminthes and Gephyrea. In a 

 postscript Dr. Eohde sums up by emphasizing that while in the 

 Nematodes the musculature exhibits the simplest form of platymyary 

 cells, from which the ccelomyary state is developed by a bending 

 round of the fibrillar plates, in the Chsetopods the simplest form is 

 that of coelomyary or the completely inclosed muscle-cells, lying in 

 a row, from which, by a secondary folding, bundles are formed, re- 

 peating in their structure the form of the ccelomyary cell. 



Development of Dasychone lucuUana.* — M. L. Eoule has some 

 notes on the development of this Sabellid, which is very common at 

 Marseilles ; its history recalls that of Psygmohranchus protensus, which 

 has been studied by Salensky, and is more direct than that of Eupo- 

 matus uncinatus, on which Hatschek has written. Dasychone lucuUana 

 begins to deposit ova early in April ; the eggs escape by the orifice 

 of its tube, connected together and protected by the voluminous mass 

 of mucus which is formed around them ; in this covering the embryos 

 pass through the early stages of their development, whence they 

 escape as trochospheres. Segmentation is not uniform, but there is 

 distinction between the more rapidly and the more slowly dividing 



* Rev. SuL Nat., iv. (1885) pp. 46o-70. 



