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D.J. GOWER AND M. WILKINSON 



posterior ends (e.g. Rathke, 1852; Tonutti, 1931; Exbrayat, 1996). 

 This loose association presumably also facilitates cloacal eversion 

 (e.g. Spengel, 1876; Wilkinson, 1990). The sheath is continuous 

 with the mesorchium and with the parietal peritoneum via a ventral 

 mesentary (e.g. Tonutti, 1933: Fig. 3a). 



A musculus retractor cloacae that is unique to caecilians origi- 

 nates on the mid- ventral body wall and inserts posterior to its origin 

 on the lateral and ventral surface of the cloaca. In those taxa 

 possessing blind sacs, the insertion is bifid and is largely or perhaps 

 entirely on the sacs themselves (e.g. Ichthyophis Fitzinger, 1826 

 Tonutti, 1931: Fig. 30e; pers. obs.; Uraeotyphlus Peters, 1879, this 

 paper: Figs. 2, 3). This muscle is thought to retract the everted 

 phallodeum when contracted (e.g. Giinther, 1864; Spengel, 1876). 



Divisions of the cloaca. The cloaca can be divided along its 

 long axis into two main regions (e.g. Duvernoy, 1 849; Tonutti, 193 1 ) 

 - an anterior cloacal chamber, or urodeum, and a posterior cloacal 

 chamber, or phallodeum (Fig. 1). The phallodeum of mature indi- 

 viduals is also broadly divisible into two regions, an anterior part 

 with pronounced ornamentation that forms the more distal part of 

 the everted phallus, and a structurally more simple posterior section 

 that forms the proximal stalk of the everted phallus. Giinther ( 1864) 

 and Wiedersheim (1879) discussed three regions in the male cloaca. 

 Their anterior region corresponds to the urodeum, and their middle 

 and posterior parts correspond to the anterior and posterior sections 

 of the phallodeum, respectively. Exbrayat ( 1 99 1 ) also distinguished 

 three regions of the cloaca, but these do not correspond directly to 

 the partitions recognised by other authors. His middle section 

 includes the posterior part of the urodeum and the anterior 

 phallodeum. 



The most obvious variations in cloacal morphology occur on the 

 internal, lumenal surface of the phallodeum, which corresponds to 

 the external surface of the phallus. The morphology of this surface 

 can be examined directly in caecilians preserved with the phallus 

 fully everted, or by dissection, serial sectioning or endoscopy 

 (Himstedt, 1996). Comparison of dissected cloacae is best effected 

 by maintaining an approximately standard approach. Figures of 

 dissected cloacae in the literature (e.g. Duvernoy, 1849; Giinther, 

 1864; Spengel, 1876; Taylor, 1968; Wake. 1972; this paper) are 

 mostly of cloacae opened with a longitudinal mid- ventral incision. 

 This procedure gives a clear view of the dorsal surface of the 

 phallodeum. Features of the urodeum must be determined by dissec- 

 tion, sectioning, or endoscopy. The caecilian phallus is sometimes 

 referred to as the phallodeum (e.g. Duellman & Trueb, 1 986), but the 

 latter term is more properly reserved for the posterior cloacal 

 chamber. The urodeum, at least in part, also contributes to the 

 phallus by forming its core as it lies inside the everted phallodeum 

 (e.g. Tonutti, 1931: Fig. 22b; this paper: Fig. 1). 



In the majority of caecilians, the distinction internally between 

 the urodeum and phallodeum is obvious in dissected specimens. The 

 relatively simple and narrow urodeum gives way posteriorly to the 

 broader phallodeum, which has pronounced longitudinal (and/or 

 oblique) ridges and deep sulci extending to the phallodeal-urodeal 

 border (e.g. see figures of Uraeotyphlus below). In most taxa, a mid- 

 dorsal protuberance marks the posterior end of the urodeum. This 

 protuberance is here termed colliculus (= little hill). The colliculus is 

 perhaps equivalent, at least in part, to the 'bourrelet' mentioned by 

 Duvernoy (1849; also Exbrayat, 1991). Typically the colliculus 

 projects into the phallodeal chamber to a varying degree, being 

 particularly large in some species (e.g. pers. obs. of Gegeneophis 

 ramaswamii Taylor, 1 942, Herpele squalostoma (Stutchbury, 1 834), 

 and Microcaecilia unicolor (Dumeril, 1864)). In species with blind 

 sacs, these open into the phallodeum adjacent to its border with the 



urodeum. A major exception to this general pattern is apparently 

 restricted to the caeciliid genera Dermophis Peters, 1879 and 

 Gymnopis Peters, 1874 (MW, pers. obs.). In these caecilians, which 

 lack blind sacs, there is no definite colliculus and no clear differen- 

 tiation between urodeum and phallodeum. Given the apparently 

 universal presence of distinct phallodeal and urodeal chambers in all 

 other caecilians, including all non-caeciliids (outgroups), we inter- 

 pret its absence as a putative synapomorphy of Dermophis and 

 Gymnopis. 



Wake (1972) made no use of a clear urodeum-phallodeum divi- 

 sion in her descriptions. She documented several features close to 

 the openings of the urogenital ducts, which are in the anterior 

 urodeum rather than the phallodeum. In our experience, this is a far 

 more irregular region in which gross morphological regularities are 

 less apparent and variation is harder to characterise than in the 

 phallodeum. Wake (1972) mostly examined partially opened 

 cloacae in which only the anterior part of the phallodeum could be 

 observed. 



The absolute and relative sizes of the urodeum and phallodeum 

 may vary taxonomically but substantial variation within species 

 might be expected given that the cloaca must serve both reproduc- 

 tive and alimentary functions. Exbrayat (1991) has presented 

 evidence of seasonal variation correlated with the breeding cycle in 

 Typhlonectes compressicauda (Dumeril and Bibron, 1841), and 

 short term changes might even occur with the passage of faeces. In 

 a sample of 1 1 preserved Hypogeophis rostratus, the phallodeum 

 ranged from 1.6 to 5.3 times the length of the urodeum (MW, pers. 

 obs.), demonstrating considerable intraspecific variation in size in 

 this species. 



Urodeum. The urodeum is a relatively simple and typically nar- 

 row chamber. Its dorsal surface is characterised by a pronounced 

 mid-dorsal longitudinal ridge (see figures of Uraeotyphlus below) 

 and seemingly irregular arrangements of other, less pronounced 

 ridges. The appearance of the lesser ridges can vary substantially 

 with state of preservation and possibly also in life. The colliculus is 

 an expansion of the posteriormost part of the mid-dorsal urodeal 

 ridge, and it shows variations in form that may be of systematic 

 value, as may differences in the overall shape of the urodeum (long 

 and narrow or short and somewhat broader). Additional lateral or 

 ventral more pronounced longitudinal ridges may also be present in 

 the urodeum (Wake, 1972). Wake (1972) described considerable 

 variation in the form of the urodeum at the points of entry of the 

 urogenital ducts, which are often depressed and may vary in their 

 relations to the mid-dorsal longitudinal ridge. She reported that 

 papillae associated with the openings of the urogenital ducts were 

 present only the typhlonectids {Typhlonectes compressicauda, 

 Chthonerpeton indistinctum (Reinhardt and Liitken, 1861) and C. 

 viviparum Parker and Wettstein, 1 929) that she examined. However, 

 one of us (MW) has observed urogenital papillae in other species, 

 including taxa that Wake reported as lacking them (e.g. Grandisonia 

 sechellensis (Boulenger. 1 909) and Geotrypetes seraphini (Dumeril, 

 1859)). Systematically useful variation may occur in the urodeum 

 but we have not yet discerned clear patterns of variation. 



Blind SACS. Blind sacs (caecal appendage of Giinther, 1864; 

 Penisblindsack of Spengel, 1876; Blindsack of Wiedersheim, 1879; 

 Penissack of Tonutti, 1931) are paired anterior extensions of the 

 phallodeum that run parallel to the urodeum (Figs. 2, 3). Blind sacs 

 vary in size and they may be free or partially fused to the adjacent 

 urodeum (e.g. Wake, 1972). In species with blind sacs, these are a 

 feature of the mature cloaca and may be absent or less well devel- 

 oped in immature males (see discussion of Uraeotyphlus below). In 

 most cases, species within the same genus, or that are otherwise 



