84 Mr. E. Raj Lankester's Zoological Ohservations 



renal organ of Gasteropods. The first portion of the alimentary 

 tube (which early appears in connexion with the primitive 

 semicircular mouth) becomes the yelk-duct. The primitive 

 mouth sinks into the yelk-bag, by the growth of its margins, 

 in a peculiar manner ; and there appears at some distance along 

 the primitive alimentaiy tube a new mouth. It seems desirable 

 to speak of these apertures ?iQ primitive and secondary mouth, 

 for the sake of description ; but it is a possibility that the 

 primitive mouth must be considered identical with the aper- 

 ture of blastodermic invagination of many Vermes and of 

 Amphioxus, discovered by Kowalewsky, and observed also by 

 me in several mollusks (Nudibranchs, Limax^ Pisidium, 

 Mytilus). 



The second fact of especial interest in the later development 

 of Loligo is the occurrence of an in-pushing from the surface 

 in the form of a groove just below (that is, posterior to) the 

 margin of each eye. A somewhat botiyoidal mass of tissue is 

 the result of this ingrowth, and gives rise, I believe (though I 

 have not definitely followed out its growth), to the optic gan- 

 glion on each side. Lateral masses of tissue are seen to dif- 

 ferentiate below the smface on either side of the oesophagus, and 

 extend to the eyes — which may become ultimately other parts 

 of the nervous system. The heart and large vessels develop 

 below the surface, also without any remarkable features. The 

 development of the mantle, gills, and cartilaginous skeleton 

 was accui-ately described by Kolliker. 



The "pen" or shell of Loligo develops in a follicle which 

 begins to form at a very early period, and remains open 

 to the surface of the mantle until the embryo is nearly ready 

 to leave the egg-case. 



An interesting phenomenon is the conti-actility of the walls 

 of the yelk-sac, which is observed at a very early period, as 

 soon as the first rudiments of eyes, ears, and mouth have 

 appeared. A rhythmic wave of contraction passes continually 

 along the wall of the sac, at that part immediately in front of 

 the alimentary tube, and doubtless acts so as to cause a circu- 

 lation of nutrient material in the direction of the young embryo. 

 The tissue which exhibits this conti'actility is of the same 

 structure (stellate cells) as that of the remarkable contractile 

 vesicle observed in the Pulmonate Gasteropods, and which I 

 have studied in Limax. It is probable that the two parts are 

 homogenous. 



I should mention that I made frequent examination of eggs 

 of Sepin^ but found those of Loligo the best fitted for study. 

 I was unable to obtain Argonauta at Naples; it is to be had 

 in quantity at Messina. 



