352 Tli e Syste m o.tic St u dy of A n n el ids. [ July, 



student of species and their general superficial relations, there can 

 be no doubt that Ehlers' group of Chaetopoda, embracing the marine 

 and fresh-water bristle-bearing worms (Boistenwurmer). the Poly- 

 chaeta and the Oligoehaeta of Grube — to the exclusion of Leeches, 

 Gephyriens. Turbellarians. and such-like doubtful orders — forms a 

 veiy convenient and well-limited field of work. 



Understanding thus, then, the term Annelids, let us see what 

 striking characteristics they present in co mm on. In the first place, 

 the body is composed of a series of more or less similar rings, from 

 which in all, a single or double series of horny bristles or hooklets 

 is developed on each side of the body. In the marine Chaetopods a 

 soft appendage, or " foot," is also developed on each side of most of 

 the rings, and three or perhaps more of these rings coalesce 

 to form a head, which in many cases is very highly organized. In 

 the earth and fresh-water Chaetopods, on the other hand, no foot is 

 eYer developed, and the head consequently has a quite simple form, 

 destitute of any tactile or sensory appendages. The modifications 

 of the head and feet (in those species possessing them) and the form 

 of the bristles or seta?, which require a microscope of high power 

 for their exam in ation, are the characters which are available for 

 generic, specific, and other divisions. It would be impossible here 

 to run through the whole group of Chaetopods, which embraces now 

 many hundreds of species ; we may, however, take one or two ex- 

 amples from Dr. ITalrugren's last published work. 



The genus Aplirod.it a, into which Linne threw all the scale- 

 bearing Annelids he knew, has been gradually broken up into nearly 

 thirty genera, grouped in four families. We have selected two 

 common species belonging to the same family, Polynoina, but to 

 different genera, for illustration: the one is the Lepidonotus stpta* 

 mains, the other the Harmothoe imbricata; they are both about an 

 inch-and-a-half in length, and frequent the same habitats, viz. the 

 under-surfaces of rocks and stones within tide-mark. These two 

 forms and the species allied to each were, till the observations of 

 Kin berg, kept in one genus, Lejyidonotus. as defined by Leach. In 

 Figs. 1 and 2 the heads of these two worms are drawn very care- 

 fully on an enlarged scale. In each there is a more or less bifid 

 cephalic lobe, carrying two pairs of eyes, and connected with a median 

 tentacle, p>t.. a pair of antennae, a., a pah' of palpi P., and two pairs 

 of tentacular or peristomial cirri, jp.c. These parts and their bases 

 are all disposed around the cephalic lobe, and form the head ; but in 

 Lepidonotus, the antennae arise from the tips of the cephalic lobe, 

 whilst in Harmothoe they spring from the base of the median 

 tentacle. A further very concise difference is exhibited by the setae 

 fixed in the soft feet, which are broader and more deeply serrated 

 in one than the other (Figs. 5, 6, 9, 10). The foot differs in each 

 a little also in the proportion of its parts. It is an example of 



