Spermiogenesis in the vermetid gastropod Dendropoma petraeum (Gastropoda, Prosobranchia)

The structure and maturation of the male gonad of the Mediterranean vermetid gastropod Dendropoma petraeum are described. Histological sections of the gonads were made throughout development and gonad activity was monitored at regular monthly intervals. During tha autumn monts the gonad is very small and is surrounded by a large quantity of connective tissue; it becomes more voluminous from December to August, with the highest growth peak in springtime. The stages of spermatogenesis were also observed and described

Sipunculus nudus: particulate components of the coelomic fluid and its relationship with brown bodies

Corpuscular components of the coelomic fluid were observed in Sipunculus nudus using cytochemical and cytoenzymatic methods. In particular, granulocytes were studied and two different types, based on morphology, chemical composition, and function were distinguished. Cell aggregates, identified as stem cells of type II granulocytes, were also evidenced. Besides, empty vesicles, vesicle fragments, laminar structures and brown bodies were observed. Based on the observation of their structure and ultrastructure, brown bodies were attributed with the function of accumulating foreign material, as well as aged components typical of the coelomic fluid

Engagement of the periesophageal ring during Holothuria polii response to erythrocyte injection.

In Holothuria polii, the periesophageal ring is an important organ supplying spherule cells after stimulation with foreign material. In animals injected with formalinized sheep erythrocytes, in fact, a depletion of spherule cells is observed in the periesophageal ring, whereas in the connective tissue, in the external epithelium and around the antigen- injected site, small, transparent cells can be visualized. It is supposed that the latter are stem cells of spherule cells