2i6 ACTIN1ARIA 



of the first order I think that I am able to draw a definite conclusion. An examination of the expansion of the 

 mesenteries on the pedal disc in four specimens namely distinctly shows, where the mesenteries of the first 

 cycle are situated. On the textfigures 202 A C I have marked these mesenteries with I. On closer examina- 

 tion of these textfigures we find that in two primary exocoels of the first order, one on each side of a directive 

 pair, one pair of mesenteries of the second order (II) and two pairs of the third (III) have been developed 

 (the fertile mesenteries are not included), while the mesenteries are more numerous in the other primary 

 exocoels. In these latter I cannot with certainty determine which mesenteries belong to the second cycle. 

 It is, however, worth noticing that the mesenteries are equally situated in all these four primary exocoels. 

 For my part, I am still inclined to suppose that the mesenteries of the second order have been doubled in 

 these four exocoels. Under this supposition the perfect pairs of mesenteries would consist of 6 pairs of the 

 first and 10 pairs of the second order. If this supposition is correct, the arrangement of the mesenteries namely 

 may be parallelled with that of the Actinostolids. On the above reproduced textfigures the different develop- 

 ment of both mesenteries of one pair of the mesenteries of the second order is not discernible at the actino- 

 pharynx, which, on the other hand, is the case at the pedal disc. On the textfigure 202 C I have designated 

 the approximate extension of the stronger mesenteries on the pedal disc with spaced-out lines. The mesen- 

 teries of the first order reach the nearest to the centre of the pedal disc, the directive pair which is turning down- 

 wards on the figure is shorter than the five other pairs. In the remaining pairs which we suppose to be of 

 the second order we see both mesenteries of the same pair differently developed. They follow the rule, char- 

 acteristic of the Actinostolids, the stronger mesenteries namely turn their longitudinal muscles towards the 

 lateral mesenteries of the first order and towards the directive pair, situated upwards on the figure; viz. to- 

 wards the oldest mesenteries, the first, second and third couple during the development. From this we may 

 conclude that the double number of mesenteries of the second cycle probably has arisen in the lateral and 

 ventrolateral primary exocoels. Supposing this to be the case, we may also explain the different development 

 of the mesenteries in one and the same pair of the mesenteries of the third cycle. Also these mesenteries 

 namely likewise follow the Actinostola-rule, though the development in the many exocoels has become more 

 irregular, probably in connection with the doubling of the mesenteries of the second order. Concerning the 

 latest developed (fertile) mesenteries it ought to be observed that I have not always been able to determine 

 a different size of both mesenteries of one and the same pair, on account of the specimens not being well pre- 

 served, the thick mesogloea of the older mesenteries causing some difficulties at the dissection, and the repro- 

 ductive organs sometimes being so strongly developed that they hide the other inconsiderable parts of these 

 mesenteries (compare below). On the textfigure 202 C I have therefore marked the fertile mesenteries as if 

 they were equally developed. I have, however, been able to ascertain that also here sometimes traces of a 

 different development of both mesenteries of the same pair are present. For all these reasons I think that 

 Sicyonis is rather nearly related to the Actinostola and Stomphia. 



Alternating with the stronger, generally sterile pairs of mesenteries (32 in the specimens 13, 33 

 in the specimens 5 and 34 in the specimen 4) there is a cycle of fertile mesenteries (fig. 202 C), which are now 

 very small and provided with few reproductive products, now longer with very large reproductive products. 

 These mesenteries arise at the pedal disc and grow upwards, but never reach the distal body-end. Exception- 



