Zoomorphology

Eakin, Richard; Martin, Gary; Reed, Carol

doi: 10.1007/BF00993301pmid: N/A

The structure of the ocelli of representatives of four of the five families of archiannelids (Polychaeta: Annelida) was studied by light and electron microscopy. The apparent photoreceptoral organelle in each species is an array of microvilli (rhabdomere). Cilia were observed in the eyes of only a couple of specimens in one species of archiannelid (Nerilla antennata). They were unassociated with the rhabdomeres; we regard them as adventitious. Support is given by this study to the theory that the photoreceptoral organelle of the ancestral annelid was a rhabdomere. Other features of the ocelli are described and illustrated.

Ferraguti, Marco; Lanzavecchia, Giulio

doi: 10.1007/BF00993302pmid: N/A

To determine the degree of systematic affinity between branchiobdellids and lumbriculids, the ultrastructures of muscle and sperm cells ofBranchiobdella pentodonta andBythonomus lemani were studied.

Harris, David

doi: 10.1007/BF00993303pmid: N/A

The mechanoreceptive and chemoreceptive hairs on the legs of the cribellate spiderCiniflo similis were examined during the moulting cycle. In mechanoreceptive hairs the new hair shaft is formed around the extended dentrites, which emerge from near the tip of the newly forming hair and continue to the old sensillum within the extended dendritic sheath. Thus there is no ecdysial canal in the base of the hair shaft as found in insect mechanoreceptive hairs. The dendritic connection with the old hair is maintained until shortly before ecdysis by which time new tubular bodies have developed in the same dendrites at the base of the new hair. In chemoreceptive sensilla the new hair shaft is also formed around the elongated outer segment of the dendrites (19 chemosensitive and 2 mechanosensitive). The two mechanosensitive dendrites develop new tubular bodies at the base of the hair. As ecdysis occurs the old dendritic sheath and dendrites are snapped off at the tip of the new hair but the pore remains open. The ultrastructural evidence indicates that the roles of the three main enveloping cells are as follows: The dendritic sheath cell secretes the dendritic sheath, the middle enveloping cell forms the hair shaft while the outer enveloping cell forms the socket. This pattern corresponds closely to that observed in insecta sensilla. The extreme length of the chemoreceptive dendrites during moulting is mentioned in connection with receptor function. The unique multi-layered nature of the middle enveloping cell is seen as a device for the formation of regularly occurring rows of small spines on the shaft of the hair.

Moraczewski, Jerzy

doi: 10.1007/BF00993304pmid: N/A

Studies were made onCatenula, a turbellarian of the order Catenulida, which had been cultured for 6 years in our laboratory. Fission begins inCatenula when the animal exceeds a specifically defined length. Neoblasts accumulate where the body wall narrows, near the subepithelial nerve cell. These cells have a large nucleus of condensed chromatin and a large active nucleolus. They have little cytoplasm, which in addition to free ribosomes, contains a small number of rough endoplastic reticular cisternae and a few mitochondria. Stem cells of epithelium were also found. These cells are similar to neoblasts, having additionally a bundle of centrioles in the cytoplasm.