THE ENTEROPNEUSTA. 657 
Ptychodera asymmetrica, n. sp. (Pl. XX XVII. figs. 1 and 9; Pl. XLVI. figs. 52, 56, 58). 
Locauity, Etc. From Hulule. According to Mr Stanley Gardiner, “Near the south islet 
is a pool with loose rocks well within the boulder zone. This form was found here in 
accumulations of sand under stones. They are remarkable in life for the enormous quantity 
of mucus they secrete, so much indeed that it is almost impossible to obtain them clean 
for preservation.” About 10 specimens were procured, mostly somewhat fragmentary. 
EXTERNAL FEATURES. A small form measuring on the average about 40 mm. in length 
(Pl. XXXVIT. fig. 1). One larger specimen, a sketch of which was made by Mr Forster 
Cooper and is reproduced on Pl. XXXVII. fig. 9, measured after preservation 60 mm. in 
length with a collar 3mm. long. This specimen however was unusually large. Two points 
about its external appearance merit attention. In the first place the liver saccules are 
somewhat small and uniformly dark in colour. There is no sharp line of demarcation between 
an anterior set of very dark caeca and a posterior set of lighter ones as in Pt. flava, var. 
laccadivensis. In the second place careful examination shews that the left genital pleura is 
always somewhat larger and more swollen than the right one. In all the eight specimens 
examined by me the gonads shew asymmetry by being developed only on the left side. 
This was the case both in a very young specimen with quite immature gonads, and also 
in the large specimen above alluded to im which the gonads were full of ripe spermatozoa. 
In his account of Pt. flava Willey (99, p. 240) mentions a case in which the gonads 
were only developed in the right genital pleura, those in the left being apparently in a 
state of arrested development. Evidently with the case of Asymmetron in his mind Willey 
writes, “Such a differential behaviour of the two sides of the body is of interest as indicating 
a tendency to unilaterality in the matter of the gonads.” Spengel (O83, p. 305) criticises 
this remark of Willey’s, regarding such a condition as produced by the presence of a 
parasitic copepod, Zve sp. In the two cases examined by Spengel where the gonads of one 
side were undeveloped the parasite occurred in the genital pleura of that side, and there 
seems little doubt that Spengel’s explanation is here correct, and that the condition is a 
pathological one. But there can be no doubt that this explanation will not hold for Pt. 
asymmetrica. The fact that in eight cases, in different stages of growth, gonads were always 
absent from the right pleura, coupled with the fact that no parasite was to be found, 
seems to shew beyond all question that unilaterality of the gonads is a feature which is 
characteristic of this species. 
INTERNAL STRUCTURE. 
Proboscis. The longitudinal muscles do not exhibit a markedly radial arrangement of 
bundles. They are strongly developed and almost entirely fill the cavity of the proboscis 
so that there is no space, or only a very small one, between them and the central complex. 
There are no-dorso-ventral muscles in front of the pericardium. The ventral proboscis septum 
does not reach to the tip of the stomochord and is often much shorter. 
The racemose organ is subject to considerable variation. It may be small and unlobulated, 
large and lobulated or not. 
There is usually a well-marked dorsal muscular decussation in the anterior part of the 
proboscis though no circular fibres pass from it ventrally. 
Collar. The cavity of the collar varies considerably. It is on the whole not large 
and may be almost absent. The collar musculature is well-developed. The dorsal septum 
