Ameboid Cells in Spermatogenic Cysts of Caecilian Testis Mathew Smita, 1 M. George Jancy, 2 M.A. Akbarsha, 2 and Oommen V. Oommen 1 * 1 Department of Zoology, University of Kerala, Kariavattom, 695 581, Thiruvananthapuram, India 2 Department of Animal Science, Bharathidasan University, Thiruchirappalli, 620 024, India ABSTRACT Sertoli cells constitute a permanent feature of the testis lobules in caecilians irrespective of the func- tional state of the testis. The developing germ cells are intimately associated with the Sertoli cells, which are adherent to the basal lamina, until spermiation. There are irregularly shaped cells in the cores of the testis lobules that interact with germ cells at the face opposite to their attachment with Sertoli cells. These irregularly shaped (ameboid) cells first appear in the lumen of the cysts containing primary spermatocytes and are continually present until spermiation. We did not observe any cyto- plasmic continuity between a Sertoli cell and an ameboid cell. Both light microscopic and TEM observations reveal a phagocytic role for the ameboid cells: they scavenge the residual bodies shed by spermatozoa. Organization of the ameboid cells is grossly different from that of the spermat- ogenic and Sertoli cells. They appear to develop from the epithelium at the juncture of the collecting ductule with the testis lobule. J. Morphol. 263:340 –355, 2005. © 2005 Wiley-Liss, Inc. KEY WORDS: caecilians; testis; ameboid cells; collecting ductules; residual bodies Caecilians (Amphibia: Gymnophiona), in view of their distribution endemic to certain tropical coun- tries, secretive, burrowing mode of life, and rarity of abundance have not been a subject of extensive in- vestigation in general, and their reproductive biol- ogy in particular is little known. Caecilians practice internal fertilization using an eversible phallodeum (reviewed in Wake, 1977). Internal fertilization in caecilians should involve special features to produce sperm and a fluid to transport them so that when ejaculated into the female tract, sperm proceed to- wards ova lodged in the oviduct and fertilize them. Aspects of spermatogenesis, spermateleosis, and sperm morphology are known for a few species of caecilians (Seshachar, 1936a,b, 1937, 1939, 1940, 1942a, 1943, 1945; Wake, 1968, 1977, 1995; Ex- brayat, 1986a,b, 2000; Smita et al., 2004a,b). A fea- ture of caecilian males is that spermatogenesis is restricted to a particular period of the year, which may be long or short (Wake, 1980, 1995). Spermat- ogenesis is cystic and any particular lobule of the testis at any time during spermatogenic activity con- tains germ cell nests (cysts) in different stages of differentiation (Wake, 1968, 1977). Sertoli cells in the caecilian testis lobules are a permanent feature (Smita et al., 2003). They are not produced as follic- ular cells in association with the primary spermato- gonia from the epithelium of the collecting ductule where it connects to a lumen in the lobule, as sug- gested earlier by Seshachar (1942b). Seshachar (1936a,b), in Ichthyophis glutinosus, and Exbrayat (1986a,b, 2000), Exbrayat and Dan- sard (1994), in Typhlonectes compressicauda, and Bhatta et al. (2001) in Ichthyophis beddomei ob- served deeply stained cells in the central zone of the lobules. Seshachar (1936a) proposed that these cells are degenerate spermatocytes or spermatogonia. However, Exbrayat (1986a,b, 2000) and Exbrayat and Dansard (1994) considered these cells to be Ser- toli cells that leave the periphery of the lobule and are pushed towards the lumen by a new generation of Sertoli cells arising from the epithelium of the ductules as follicular cells. These cells, when pushed further into the lobule, decrease in volume and al- ways surround developing germ cells. At the end of the cycle they degenerate and flow to the evacuative ductule to lie amid the spermatozoa. Thus, two kinds of Sertoli cells were proposed, peripheral and central, the latter discharged from the wall of the lobule and lying loose in the lumen (Exbrayat, 1986a,b, 2000; Exbrayat and Dansard, 1994). We recently reported that there is only one kind of Sertoli cell in the testis lobules of Ichthyophis tri- color and Uraeotyphlus cf. narayani (Smita et al., 2003). These cells rest on the basement membrane of the lobule. They are extremely tall and exten- sively hypertrophied, so that they fill the entire lob- ule. They frequently form a lumen or lumina between/among themselves to provide space for po- Contract grant sponsor: University Grants Commission, New Delhi; Contract grant number: F.3.33/2002 (SR-II) (to O.V.O., M.A.A.); Con- tract grant sponsor: DST, New Delhi (FIST programme). *Correspondence to: Dr. Oommen V. Oommen, Professor and Head, Department of Zoology, University of Kerala, Kariavattom, 695 581, Thiruvananthapuram, Kerala, India. E-mail: oommen@bigfoot.com Published online 1 February 2005 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jmor.10310 JOURNAL OF MORPHOLOGY 263:340 –355 (2005) © 2005 WILEY-LISS, INC.