124 
ME. H. N. MOSELEY ON THE ANATOMY AND 
hence there appeared to be a wide gulf fixed between the Planarians and their really 
very near allies the Leeches. A study, however, of the muscular arrangement of 
Bipalium and Bhynchodemus shows that in these animals the muscular arrangement is 
almost identical with that in the leech ; and, further, that that which exists in the lower 
Planarians and also in the Nemertines is easily reducible to the same type. 
In Bipalium and Bhynchodemus the muscular arrangements are of very great com- 
plexity, and may be regarded as belonging to two systems, superficial and deep. The 
general arrangement of each system will first be considered, and then the special 
arrangement found to exist in the ambulacral line, this being a purely muscular organ, 
and therefore properly described in this place. The special muscular arrangements 
which hold in the generative and digestive organs will be described under the headings 
of these systems. 
Superficial Muscular System. — Immediately beneath the thin basement membrane of 
the epidermis of Bipalium and Bhynchodemus is a layer of closely apposed muscular 
fibres. This layer is clearly to be distinguished all over the body ; but it varies in thick- 
ness in different regions, and also in the arrangement of its fibres, although the general 
trend of these latter is always circular. This layer may be seen in Plate XI. fig. 1 
(E. C. M.) or, with its fibres seen in section, in Plate XV. fig. 9 (E. C. M.). It is thickest 
on the dorsal region, and inferiorly on each side of the ambulacral line. In these 
regions also the arrangement of its fibres is most complex : this arrangement is dis- 
played diagrammatically in Plate X. fig. 13; a sort of basketwork of fibres running in 
three directions is formed; and an almost exactly similar arrangement of fibres is 
described as existing in the external muscular coat of higher worms, in the leech and 
Nematodes, by Leuckart (loc. cit. pp. 459, 645). When this muscular coat is viewed 
from above, the fibres are seen crossing one another diagonally, whilst others take a 
directly transverse or circular course (Plate XI. fig. 5). 
The decussating* fibres are thus doubly oblique in their direction. At the sides of 
the body this muscular coat is almost entirely absent, and especially in Bhynchodemus 
(Plate XI. fig. 2). The muscular coat appears to be almost homogeneous and structure- 
less ; in fact it exactly resembles the external coat of aquatic Planarians, such as Lepto- 
plana tremellaris (Plate XIY. fig. 1, E. C. M.) or Bendroccelum lacteum (Plate XI Y. 
fig. 7, E. C. M.), though in this latter instance the external coat is more evidently mus- 
cular. Now the remarkable arrangement of fibres which is common to both groups 
being taken into consideration, there can be little doubt that the external circular 
muscular coat here described in Bipalium and Bhynchodemus is the homologue of the 
similar external coat of the leech ; and it is evident that the external coat of Bendro- 
ccelum lacteum answers to that of Bipalium , and that of Leptoplana tremellaris to that 
of Bendroccelum lacteum . The body investments are essentially homologous ; but mus- 
cular elements are developed in them more perfectly in some forms than in others, and 
in some parts of some forms more perfectly than in other parts. In higher worms the 
development of fibres is almost constantly perfect in all parts of the body. Kefersteiist 
