230 SUMMARY OF CUREENT RESEARCHES RELATING TO 



body, and is for a great part ciliated ; the ciliation resembling exactly 

 that of ^olosoma quaternarium. 



The blood-vascular system exhibits a very low degree of develop- 

 ment, consisting of a dorsal and ventral trunk, which extends through 

 the whole length of the animal ; the former gives rise, in the first 

 segment, to a short transverse trunk, from which arise two lateral 

 trunks. The blood is yellow and non-corpusculated ; the walls of 

 the vessels are formed by a fine structureless membrane in which 

 nuclei are imbedded. Distinct pulsations could not be detected, 

 though there was a regular current. A structure, comparable to the 

 solid cord of cells in the interior of the dorsal vessel, described by 

 von Kennel in Ctenodrilus pardalis, is here also present ; both these 

 may be compared with the darkly- coloured organ found by Claparede 

 in Cirratulus, Terehella, and others. 



The head is made up of the cephalic lobes and oral segment, and 

 is distinguished from the metameres which succeed it by its relatively 

 greater length and the possession of the very characteristic proboscis, 

 of the tentacle, and of the segmental organs. The coelom, as in 

 C. pardalis, extends into the cephalic lobes. The whole of the ventral 

 surface of the head is ciliated, and these cilia serve to drive currents 

 of food to the mouth of the worm. The author regards the head as 

 essentially different from all the succeeding segments. The proboscis 

 lies beneath the mouth, and consists of a solid, muscu]ar, broad plate ; 

 it opens into a chamber common to it and the mouth and has 

 apparently the function of a locomotor organ. 



The resemblances to Polygordius which this new form exhibits are 

 emphasized by the possession of a single tentacular organ, the fellow 

 of which seems to have been lost in the course of time. It arises 

 just below the proboscis, and is capable of doubling its length ; owing 

 to the possession of a special musculature, it can also become con- 

 siderably diminished. It is distinguished from the tentacle of 

 Polygordius by the absence of a diverticulum of the coelom ; it is 

 marked externally by a ciliated groove, the cilia of which work 

 towards the body ; it appears to be not only a tactile organ, but also 

 to bring food to the mouth. Individuals with two tentacles are not 

 rarely seen. 



Like G. pardalis, C. monostylos has only one pair of segmental 

 organs, and these are placed in the head ; they are coiled, finely 

 granular tubes, and the cilia around the coelomic orifice are very deli- 

 cate. In the nervous system the new species considerably resembles 

 the already-described species of the genus; the dorsal ganglion is 

 placed in the cephalic lobes, and its central mass is dotted ; the 

 ganglionic cells are only indistinctly separated from the surrounding 

 epithelial cells; the ventral cord is not provided with metamerically 

 arranged ganglia, but forms a simple well-developed cord, which 

 extends through the whole length of the body ; in very thin sections 

 indications of a fine median membrane were occasionally detected, 

 but no peripheral nerves could be made out. The nervous system 

 remains in the hypodermis. Cells of peculiar character, and appa- 

 rently of mesodermal origin, are to be found floating in the coelom. 



