118 Abdomen in Ricinulei 



3. The Abdomen. 



Whilst Guerin-Meneville and Westwood cautiously state that the abdomen appears to 

 consist of four segments, Karsch (c, p. 30) gives this number without hesitation. Thorell 

 indicates besides the same four segments also a " segmentum anale," of which, however, he 

 says {h, p. 13) that he is uncertain whether it ought to be looked upon as formed by the 

 coalescence of the tergite and sternite of a fifth segment. What he describes as " segmentum 

 anale " is a small protuberance at the posterior extremity of the abdomen, on which the 

 anus is placed, or rather, as we shall see, appears to be placed. — We have on the contrary 

 distinguished nine segments with certainty. On morphological grounds it must be considered 

 possible, though little probable, that in reality one more segment enters into the composition 

 of the abdomen, but if so it is not discernible. Our starting-point in the sequel, as well 

 as in the Latin description of the species, will therefore be that number which we have 

 actually found. That our predecessors have not found more than four or five segments is 

 easily explained, because the others are very difficult to distinguish, and because the difference 

 between the segments as regards size is so great, three of them, the fourth, fifth and sixth 

 (the second to the fourth of earlier writers) being very large, the third rather large, whilst 

 the other's are small or even very small, and parti}' hidden. 



The tergites of the fourth, fifth and si.xth segments are each divided into three areas, 

 of which the middle one is the largest. These areas, as well as the tergites themselves, 

 are in young animals separated from each other by a broad, softer and more light-coloured 

 connecting membrane which, however, is of extraordinary thickness, and therefore scarcely 

 allows much movement of the pieces. It is an interesting fact that the granules of which 

 so great a multitude adorn the tergites of these animals occur also, though in smaller 

 numbers, both on the connecting membrane between the tergites themselves, and on the 

 lateral membrane connecting the tergites with their sternites — a feature which, as far as wc 

 know, recurs only in Thelyphonoida;, and, to a small degree, in Phrynoid;e, where it may 

 be observed in the latei-al connecting membrane between the tergites and the sternites. 

 By degrees, as the animals grow in size, the interstices between the tergites, as well as 

 between their middle and lateral areas, diminish, and in adult specimens they ai'e found 

 almost coalesced, the connecting membrane appearing only in the shape of quite narrow strips. 

 The sternites of the fourth, fifth and sixth segments are not divided into areas (PI. VII., 

 fig. 1 b), but the connecting membrane between them is very thick and tough, and becomes 

 narrower with age, as in the case of the tergites, until the sternites of these three segments 

 coalesce with each other and with that of the third segment so as to form a ventral shield, 

 on which the boundaries between the segments are marked only by feeble transverse lines ; 

 the boundary between the third and the fourth sternite is more strongly marked (PL IX., 

 fig. 1 g), particularly towards the sides where it appears as a somewhat deeper groove. Both 

 on the tergites and on the sternites of the fourth, fifth and sixth segments a pair of 

 depressions are noticeable, as on several segments in Phrynoidse'. These correspond to the 



^ In 2»f«opftn/nus2)a7»natus (Hbst.) Kraep. six pairs of such marked on the outside by these depressions on the fifth to 



depressions exist on the tergites of the third to the eighth the eiglith segments extend from the dorsal to the ventral 



segments ; four pairs of corresponding depressions are seen surface, and a similar pair of muscles exists in the fourth 



on the sternites of the fifth to the eighth segments. The segment, although their points of insertion on the inside of 



four pairs of muscles of which the points of insertion are the sternite are not visible outside ; but the muscles which 



