HISTOLOGY OF THE LAND-PLANARIANS OF CEYLON. 
135 
by stout muscular fibres. These canals, however, subserve in this animal all the pur- 
poses of imperfect circulation required, and even, by means of their branches, may effect 
the erection of the penis, and perhaps also the distention of the pharynx (Keferstein, 
loc. cit. p. 21), as do the blood-vessels of higher forms. 
This primitive vascular system, which in Tcenia and Bothriocephalus assumes a very 
definite and tubular form, though still occupied internally by spongy tissue, is directly 
homologous with the body or perivisceral cavity, which is persistent throughout life in 
JBranchiobdella , and present in all leeches at some period of development, and in all 
adult leeches, in a rudimentary condition at least (Leuckart, Die menschl. Paras, p. 666). 
The true blood-vessels are, when present, developed within and partitioned off from this 
primitive vascular system. In Tcenia and Planarians no such further development has 
taken place. The nervous system lies within the primitive vascular system ; but when 
blood-vessels are developed, the nervous system is often included within the latter. In 
some animals there are further developed, from without inwards, ciliated tubes, sacs, or 
pores, which communicate with the primitive vascular system, by me.ans of which excre- 
tion from the vascular system takes place ; and such an arrangement reaches its highest 
development in such forms as the Trematodes. It is, however, erroneous to consider 
the main and necessary function of the primitive vascular system as excretory, since in 
such forms as Bvpalium it obviously performs many other circulatory functions, although 
here, as in Trematodes, it may also subserve an excretory function by means of the 
ciliated sacs in the region of the head. Mertens {loc. cit. p. 12, 1833) describes the 
ganglia of Leptoplana as hearts, and the nerves given off from them as vessels. Duges 
held a like opinion {loc. cit. 1, 1 828). It seems highly probable that this is to be explained 
by the fact that the nerve-ganglia of this Planarian, and probably of all others where 
such exist, lie within a vascular sinus, a part of the primitive vascular system, and in 
continuation with it, the sinus giving off branches in which the nerve-branches lie. I 
cannot agree with Keferstein in supposing that Blanchard’s injection of the sinus 
round the ganglia of Lejptoplana and its branches resulted from unskilful manipulation, 
and does not represent the true state of the case (Keferstein, loc. cit. p. 21). I had 
only one spirit-specimen of Leptoplana available for examination ; but in this the ganglia 
were seen on section to be surrounded by a space occupied by loose spongy tissue, very 
little stained by carmine and exactly resembling that seen in the vessels of Bipaliitm , 
and the nerves occupied broad tracts of similar appearance ; and on a vertical transverse 
section being made of the body, the two canals filled with spongy tissue were cut across, 
exactly resembling those of Bothriocephalus in structure, and coinciding in position with 
the large pair of longitudinal body-nerves. Quatrefages (Sur les Planaires, p. 172) 
says the brain is placed in a cavity or lacuna, prolongations of which accompany the 
viscera. He figures no regular water-vascular system apart from this. It is especially 
to be remarked that, almost invariably, observers who figure the nervous system of 
Planarians distinctly, do not in the same animal give the vascular system, and vice versa. 
Thus Oscar Schmidt (Zeitschrift fur wiss. Zool. x. 1859, p. 29) speaks of seeing in a 
