Memoirs: On the Structure of the Nephridia and ‘funnels’ of the Indian Leech Hirudinaria with remarks on these organs in Hirudo

Abstract

1. The nephridial system of Hirudinaria consists of a series of seventeen pairs of nephridia metamerically arranged in somites VI to XXII. The first sis pairs occur in the pretesticular segments (VI-XI), while the remaining eleven pairs lie in the testicular segments (XII-XXII). 2. A typical nephridium consists of the following parts: (i) the initial lobe, (ii) the apical lobe, (iii) the inner lobe, (iv) the main lobe, (v) the vesicle-duct and the vesicle. All the nephridia in the testicular region possess ‘funnels’ (ciliated organs) which are enclosed within the ampullae of the perinephrostoniial sinus. There is no continuity or connexion of these ‘funnels’ with the nephridia in the adult leech. 3. The inner end of the initial lobe is directed towards the testis-sac and either ends freely within the connective tissue without coming in contact with the testis-sac, o r- is embedded in fibrous tissue in external contact with the wall of the sac, or becomes incorporated within the outer wall of the perinephrostomial sinus. 4. The initial lobe (testis-lobe) forms a very long coiled string of cells round the apical lobe and part of the inner lobe. The inner lobe (the ‘recurrent lobe’ of Bourne) forms a distinct strip of nephridial tissue enclosed between the two limbs of the main lobe besides a small piece which runs alongside the apical lobe. The inner lobe canals serve to connect the intra-cellular canals of all the lobes with one another. 5. The cells of the different lobes of the nephridium are tunnelled through by intra-cellular canals and canaliculi which form a continuous branching network throughout the body of the nephridium. Besides, there is an intra-cellular central canal which makes 1 3/4 ‘rounds’ through the various lobes of the nephridium and opens into the vesicle. The intra-cellular canals and canaliculi open directly or indirectly into the central canal. 6. The vesicle has no muscular layer, and its wall is not contractile. The evacuation of the contents of the vesicle is brought about by the contraction of ventro-lateral mameles of the bodywall that extend across all the resides. The vesicle and the terminal excretory duet do not develop from the rudiments of the true nepfaritliam, but are formed from an ingrowth of the epidermis. 7. A fully developed adult ‘funnel’ (ciliated organ) is a compound structure consisting of (1) a central reservoir and (2) a large number of small independent funnels set on the reservoir and opening into it. The funnels are profusely dilated. Each funnel is composed of five to six cells, and has the appearance of an ear-lobe with a broad distal and a narrow proximal end. 8. The reservoir is the seat of manufacture of corpuscles which are thrown out of the reservoir through the funnels into the surrounding sinus by the active movements of the cilia of the numerous funnels. 9. The ‘funnel’ is not a degenerate structure. It has, infact, multiplied into numerous small ciliated funnels, which, are much more effective in their ciliary action than a single funnel, even of a large size, could be. Cilia of the funnels show very vigorous movements which keep the fluid in the sinus in constant active circulation. The ciliated organ, instead of serving a renal excretory function, has here become subservient to the sinus-system. 10. The botryoidal vessels are in direct communication with the perinephrostomial sinus. Possibly the corpuscles take up pigment and become the chloragogen cells in the botryoidal vessels. 11. In the embryonic condition the ‘funnel’ is a solid mass of cells which is distinctly continuous with the nephridinm by means of a delicate strand of cells. This connexion of the ‘funnel’ with the nephridium snaps later, and the two become discontinuous and discrete structures. In the embryonic solid ciliated organ the funnel-forming cells can be clearly distinguished from the cells of the reservoir. The ‘funnel’ becomes enclosed at an early stage in the perinephrostomial sinus, which is a part of the reduced coelom. 12. The nephridial system of Hirudo is essentially similar to that of Hirudinaria. In Hirudo the initial lobe does not coil round the apical lobe, but forms one mass round the ampullae of the perinephrostomial sinus and another between the apical and main lobes. The inner end of the nephridium is closed as in Hiradinaria. The ‘funnels’ have the same structure and perform the same function as in Hirudinaria.