*iournl'i.Tay !?i8m ] t^^& Ecouomij of Stephanocevos. 247 



compelled nevertheless to admit that " they are not directed in an 

 exploratory manner from side to side," like the antennas of insects. 

 Dujardin states that " no trace of the entrance or exit of water is 

 perceptible even when particles of colouring matter are diffused 

 through the hquid calculated to indicate the slightest current ; " and 

 Perty, Gosse, Huxley, and Leydig coincide as to their non-perforated 

 character. 



Admitting at once the non-perforated character of these organs, 

 the foregoing arguments offer themselves as corroborative evidence 

 in proof of their being subservient to respiration. Now, the antennas 

 of the tube-building Botifera are not only first exposed in emerging 

 from the tubes, but they alivays remain exposed to the water, even 

 during the animal's retreat. Once aware of their existence in Flos- 

 cularia coronetta, this fact became most manifest ; so that while other 

 functions may be suspended, that of respiration, which is vital in the 

 higher animals, is permitted to continue uninterrupted. 



It is not necessary that these organs should be i:)erf orated to 

 admit water from without, this, being of a different density to that which 

 permeates the vessels of the body, would enter the tubes or tubercles 

 by the process of Endosmosis. Leydig adopts this hypothesis, but 

 hampers his conclusions with the assumed necessity for palpable 

 orifices. Endosmosis operates through membranes such as even the 

 blood-vessels of the slug having a layer of chalk; through the more 

 delicate membranes of the capillaries ; and with animals that exist in, 

 and respire an element abounding in particles whose intrusion or 

 contact would be detrimental, if not fatal to the due performance of 

 the process, the general integument of the animal may be impervious 

 to its action, while these protuberances may be specially constituted 

 to promote it, under the protection from accident these accompany- 

 ing bristles are eminently calculated to aflbrd, so as to ensure the 

 uninterrupted action of Endosmosis, whose gentle and constant 

 operation of molecular intrusion would create no current sufficient 

 to influence anything so gross as visible particles of colouring 

 matter ; while on the other hand the fluid thus induced and circu- 

 lated by the agency of the pulsations, collects in, and after inflating 

 the cloaca, is discharged by the intermittent action of systole, which 

 has heen observed in the case of Notommcda to disturb the adjacent 

 particles of floating matter by a palpable jet d'eau. 



It would therefore appear that these processes involving motions 

 must be of necessity dependent on some force ; and seeing their in- 

 timate connection with the hrain, we may safely assume them to be 

 due to nerve force. The hraifi has been referred to as such, and 

 also as a ganglion. It is seated in the anterior regions in a dorsal 

 aspect ; it is pear-shaped, constricted in the middle, where it sup- 

 ports certain small processes which traverse its substance as well as 

 project beyond (Figs. 1, 2, k). In active individuals the brain is 

 large and prominent, but less conspicuous in others whose sluggish 



