62 SUMMAEY OP CURRENT RESEARCHES RELATING TO 



a single layer of longitudinal muscular fibres, which are not divided 

 into arese, though they are found at regular distances all around the 

 animal. The mesodermal tissue between the musculature and the 

 enteron is, likewise, very slightly developed ; in connection with the 

 peritoneum there is a thin layer of small cells in which gemmation 

 may be seen ; this, which may be looked upon as undifferentiated 

 mesoderm, is most largely developed in the region of the dissepiments. 



The stomach and intestine are formed by a single layer of large 

 epithelial cells ; all the cells of the intestine are ciliated. The circu- 

 latory system is not closed, and presents a greater simplicity than 

 that known in any other Annelid ; a thin membrane, with scattered 

 spindle-shaped nuclei, forms the wall, and has no thickenings or 

 additions even in the dorsal contractile portion ; on the other hand, 

 we find in this dorsal vessel a solid cord of cells, the function of 

 which must remain very obscui-e, unless we are allowed to regard it as 

 a hsematopoetic organ ; it may be compared with the structui'e noted 

 by Claparede in Terehella. 



There is but one pair of segmental organs, lying directly behind 

 the pharynx, and, as it seems, in the first, or, at least, in the second 

 segment. Their walls are extraordinarily thin, and their lumen of 

 pretty much the same width throughout. 



The account that has been given will be sufficient to show that in 

 Ctenodrilus we have to do with an ancient and " collective " type 

 which exhibits affinities to the Oligochaeta on the one hand, and the 

 Polychseta on the other ; the very forward position of the segmental 

 organs forbids us to look upon it as a degraded form. For its reception 

 there may be formed a family Ctenodrilidce, consisting of small marine 

 Annelids, of a few segments, with two pairs of setae, a non-closed 

 blood-vascular system, the dorsal vessel lying in the first body- 

 segments, and opening into the coelom in the first trunk -segment. 

 A single pair of segmental organs in the head. Eeproduction by 

 division with gemmation. Sexual reproduction unknown. Ctenodrilus 

 and Parthenope the two known genera. 



The rest of the paper is occupied by an account of the phenomena 

 of gemmation. 



Distichopus.* — Prof. J. Leidy describes a new genus of Annelids — 

 Distichopus, closely allied to Enchytrceus, but with setapeds in a single 

 row on each side ventrally, and not double as in the former genus. 



Turriform Constructions by Earth-worms.f — In his work on 

 worms, Darwin has described some tower-like dejections which he 

 never saw constructed in England, but which are attributed to an 

 exotic species of Perichceta from Eastern Asia, naturalized in the 

 environs of Nice. E. L. Trouessart has lately observed similar dejec- 

 tions in gardens near Anglers. Having collected a large number of 

 worms from where the towers were made, he found no species of 

 Perichceta, nor of any other exotic genus. In two or three cases he 

 surprised the worms at work, and they were Lumbricus agricola. 



* Proc. Acad. Nat. Sci. Philad., 1882, pp. 145-6. 

 t Comptea Rendus, xcv. (1882) p. 739. 



