IS EINAR LÖNNBERG: NOTES ON SPIRULA RETICU1 \I V OWEN 



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destroyed, we cannot determine whether it has been sensory by nature or not. i 

 muscles which are able to alter the form and the volume of the lenticular i 

 may have the function of regulating the tension of the organ to adju 

 impression it is to receive at each moment. It remains however tobe decided what 

 kind of impressions the organ is constructed to receive, and on this point only 

 supposition can be at present thrown out. This is essentially the case for we cannot 

 possibly understand the senses requisite for a life like that Spiraln leads in the 

 depths of the sea. But as Spirula possesses a polythalamous shell whi« h seems fitted 

 to be a hydrostatic apparatus, one might venture a guess that this organ possibly 

 has the function of helping the animal to apprehend the hydrostatic pressure, and 

 so to be able to regulate the apparatus in time which otherwise would carry it to 

 the surface, and to death. 



This organ seems quite characteristic for Spirula and there is no doubt that 

 it is developed in that animal originally and alone, for no other Cephalopod pos 

 ses any organ that can be suspected as a homologue, except perhaps the aboral bi 

 of Sepiella. That organ however has quite a different function, being plainly a gland 1 . 



In many respects Spirula must be regarded as an archaic type that 

 branched off at a very early date from the ancestors of the dibranchiates. I'i 

 neer (1. c. p. 31) writes: "Spirula must have come from a Belemnite-like form, still 

 without rostrum as (Belenvnoteuthis) ; the right phragmoconc of which, still external 

 (at least in part), is rolled up in an inverse sense to that of Nautilus" and in his 

 phylogcnetic table (p. 32) he makes the Spirula-bvAwch. diverge from a point above 

 the Belemnoteuthis-iovm. I think we must try and find the ancestors of Spirula still 

 further back at a time prior to the development of Belemnotcuthis, if the two ar< 

 lated to each other at all. The shell of Belemnoteuthis is already very much red 

 from the original external shell of a primitive form and in the thickened wall of the 



1 This bursa opens at the aboral end of the body on the dorsal (sometimes ventral) side and 

 lies ju-t between and behind the two fins, having a transverse or roundish pore. In .' 

 HASSELT the inner side of the bursa has a system of "plicis plurics divisis et in- 

 very suitably describes it {"Septella Grav. Sit.", Vid. Meddel. nat. loren. Kjöbenhavn 1880, p. 347 

 It has a reddish colour. By studying sections through the bursa we find that the plica are covered wit) 

 very high columnar epithelium with the nuclei in the basal part of the cellules which are plainly 

 The interior of each plica consists of a lamella of connective tissue, containing al 

 merous rather strong muscles. The walls of the bursa are furnished with an outer 

 sal muscles and an inner one, less thick, of longitudinal muscles. Towards the pore the I 

 be still stronger, and to increase in number. The bursa is limited by a fibrous sac. which 

 for the most part, almost directly upon the shell, but posteriorly leaves a little int. i 

 As can be seen, the structure of this organ is quite different from that of the "aboral i 

 nor is its function the same either. The bursa at the aboral end of Sepiella is a gland, but the use 

 gland is unknown. 



