Fig. 4. A in Morphogenetic gradients in graptolites and bryozoans

Fig. 4. A. Variation of morphological characters of zooidal tubes (thecae) along the colony axis in Cucullograptus aversus Urbanek (A1), details of structure of apertural apparatus within the proximal, medial and distal thecae (A2–A4). B. Pristiograptus dubius (Suess), thecae with growth bands shown diagrammatically. A is a biform type with the strongest expression of characters in the distal part of the colony, while B is a uniform type exhibiting mainly the size gradient. Not to scale. From Urbanek (1973).