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The aim of the present study is to describe the organization of the ovary and mode of oogenesis at the ultrastructural level in two representatives of Lumbriculida -Lumbriculus variegatus and Stylodrilus heringianus. In both species studied, the ovaries are small and conically shaped structures that are attached to the intersegmental septum via a thin ligament. The ovaries are composed of germline cysts formed by germ cells interconnected by stable cytoplasmic bridges. As a rule, the cyst center is occupied by a poorly developed anuclear cytoplasmic mass, termed a cytophore, whereas the germ cells are located at the periphery of the cyst. Germline cysts are enveloped by somatic cells. The ovaries of the species studied are polarized, i.e., along the long axis of the ovary there is an evident gradient of germ cell development. The data obtained suggest ovary meroism, i.e., two categories of germ cells were found: oocytes, which continue meiosis, gather nutrients, grow and protrude into the body cavity, and nurse cells, which do not grow and are supposed to supply oocytes with cell organelles and macromolecules via the cytophore. The ovary structure and mode of oogenesis in the species studied were compared with those of other clitellate annelids. As a rule, in all clitellates studied to date, the ovaries are composed of germline cysts equipped with a cytophore and associated with somatic cells; however, the ovary morphology differs between taxa regarding several quantitative and qualitative features. The ovary organization and mode of oogenesis in L. variegatus and S. heringianus strongly resemble those found in Tubificinae and Branchiobdellida studied to date. Our results also support a sister-group relationship between Lumbriculida and a clade comprising ectoparasitic clitellates (i.e., Branchiobdellida, Acanthobdellida and Hirudinida) with Branchiobdellida as a plesiomorphic sister group to Acanthobdellida and Hirudinida., (Copyright © 2013 Elsevier GmbH. All rights reserved.)

In this paper we report for the first time the results of histology of the golden loach (S. baltica) gonads (25 females and 8 males) and absolute fecundity of females from the Bug River during the reproductive season. The golden loach has an asynchronous ovary and spawns in batches. The absolute fecundity of the golden loach ranged from 1507 to 7220 eggs (3050±1377). We hypothesize that the golden loach spawns twice a year.

This is the first study concerning the features of the reproduction process of the karyologically identified spined loach C. taenia (2n=48). The histology of 71 ovaries, and gonadosomatic index (GSI) of karyologically identified spined loach Cobitis taenia L. from Lake Klawój (Northern Poland) were examined. The absolute and relative fecundity of 25 females was estimated by gravimetric method. The age of fish was determined according to the annual increments of otholits. The spawning of C. taenia from Lake Klawój took place from May to July, at a water temperature exceeding 18.5 degrees C. The GSI values at the beginning of the reproduction period ranged from 7 to 19%. The average absolute fecundity of females was 2078 eggs, with the number ranging from 869 to 3371 eggs. High individual variability in the gonad histology and the GSI values during the reproductive period was observed. Such variability could be the result of beginning the reproduction process in the fish at various times and, probably, due to the various numbers of batches laid and various numbers of eggs per batch.

The aim of the conducted research was to establish postpartum oestrous cycles and approximate data for mating Polish Merino sheep. 34 sheep were examined. During sheep laparotomy observations of ovaries and uterus were made on definite days of the postpartum period (1-78). It was stated that after about one-week of postpartum inactivity, the growth and development of follicles occurred in ovaries. First ovulations were noticed from the 15th to 18th day of postpartum, while processes connected with uterus involution were not completed. From the 14th to 18th day of postpartum, casting off of pregnant tissues from caruncules' surfaces into uterus cavity occurred. In the majority of sheep, regeneration of caruncules and purification of uterus cavity were completed by the 30th day of postpartum. The observed compatibility of the phases of ovary cycle with macromorphologically determined functional state of uterus after 30 days of postpartum, in the majority of tested sheep, suggests possibility of successful mating of Polish Merino sheep.