§ 2.122 ENDOCRINE GLANDS FROM ECTODERMAL EPITHELIUM 39 



but this substance also passes into the blood, to affect the chroma- 

 tophore muscles (§ 3.21), probably by an indirect action. 



The glands, of which there are two in decapod and four in 

 octopod cephalopods, arise from the stomodaeal ectoderm, with 

 which they retain their connection as a duct to the mouth. It is 

 the posterior (or dorsal) pair which secretes tyramine in Eledone 

 moschata and in the two species of Octopus which have been 

 investigated (Bacq and Ghiretti, 1951). 



2.122 Corpora allata of Insecta 



The CORPORA ALLATA are endocrine glands, the cells of which 

 arise in development as a pair of small ventrolateral invaginations 

 near the base of the first maxilla (Fig. 2-8). Thence the tissue 

 migrates inwards to lie between the oesophagus and the aorta ; it 

 may remain paired, or the two parts may fuse more or less com- 

 pletely. Each part is supplied with neurosecretory axons passing 

 on from the corpora cardiaca, which lie just in front of them 

 (Fig. 2-9). 



There is evidence that these axons must remain intact if they 

 are to control secretion by the corpora allata, as though their action 

 were either nervous or due to a neurohormone diffusing from cell 

 to cell rather than being carried in the circulation. The corpora 

 allata are also connected with the stomatogastric system by nerves 

 from the hypocerebral ganglion. 



The densely packed cells of the corpora allata show cyclic phases 

 of secretion and multiplication, coinciding with their cyclic activity 

 in controlling the "juvenile" character of nymphal and larval 

 moults (Part II, § 3). A new phase of activity starts very soon after 

 each moult is completed: at first the gland is small and the cells 

 are all alike ; then there is a burst of mitotic activity followed by an 

 increase in size of some cells, leading to increase in gland size. 

 The larger cells, which have much larger nuclei than the undiffer- 

 entiated cells, then begin to form their secretion. This appears 

 first as granules in the cytoplasm ; it then accumulates in vacuoles, 

 which can later be seen to lie outside the cells in intercellular 

 spaces. From this position the secretion, or the hormone released 

 from it, presumably passes into the blood stream at the critical 

 period for controlling the next moult. Some of the secreting cells 



