STUDIES ON THE TURBELLARIA. 431 
perhaps poisoning, the relatively large and often active 
animals on which this Turbellarian preys. 
The muscular layers present no features calling for special 
remark. As in all the Accela hitherto described, there are 
three layers—an outer circular, a middle diagonal,’ and an 
inner longitudinal. In addition, there is an abundantly- 
developed system of parenchyma-muscle, chiefly composed of 
dorso-ventral fibres. 
The Alge.—The symbiotic Alge, in the full-grown 
animal, form two dense strata—one dorsal, the other ventral— 
just within the muscular layers. But they are by no means 
confined to these situations, occurring, often in abundance, 
all through the cortical parenchyma, and between the cells of 
the ovaries and the lobes of the testes. They also occur, 
though rarely, in the digestive parenchyma (fig. 7). In the 
smallest specimens, just escaped from the egg, only one or 
two of the Alge are to be found; but they appear to multiply 
rapidly by fission, as somewhat larger specimens of the worm 
contain large numbers. ‘They are, apparently, simply em- 
bedded in the parenchyma, and are not contained in the 
interior of cells. Sometimes they are isolated, more commonly 
they adhere together in irregular strings; but in the latter 
case the adhesion is very slight, and, when the host is 
crushed or broken up, the algal cells become detached from 
one another. 
The Algee (fig. 6) have an average diameter of ‘025 mm. 
They have a very definite shape—oval, with the broader end 
rounded and entire, and the other end usually with a distinct 
incision or notch, which may be double. 
An important feature distinguishing this Algz from that 
which occurs in Convoluta? is the presence of a distinct, 
though somewhat thin, non-protoplasmic cell-wall. This 
becomes very clear in stained cells, particularly when plasmo- 
lysed. It does not respond to the iodine and sulphuric acid 
‘ In the figures of sections these diagonal fibres are not represented as 
distinct from the circular. 
2 Haberlandt (in 15), Gamble and Keeble (8). 
