748 J. H. ASHWOKTFT. 



thickness of the egg 0*07 mm. In A. cristata the three 

 axes of ova removed from a ripe female in Naples measure 

 0"155mm., 0"1 lo mm., and 0"07 mm. respectively.^ The ova of 

 A. grubii and A. ecaudata are not compressed in this way, 

 or only very slightly so. They are usually ovoid, and ripe ova 

 of the former species are 0'17 mm. long and 0'15 mm. broad 

 and thick. The largest ova of A. ecaudata which I have seen 

 have slightly smaller dimensions, but they are pi'obably not 

 quite mature. The ova of A. grubii and A. ecaudata are 

 distinguished by their stout vitelline membrane, which is 5 

 to 6 /i thick; while in] A. claparedii, A. cristata, and A. 

 assimilis it is 2 to 3 f.i, and in A. marina only slightly over 

 1 /t in thickness. 



Brain. — The brain of A. assimilis conforms to the 

 general plan seen in the marina section of the genus. It 

 consists of a pair of anterior lobes placed well forward in 

 the prostomium, a pair of posterior lobes which lie below the 

 nuchal organ, and an intermediate region which connects the 

 anterior and posterior lobes. The anterior lobes are short 

 but very broad ; in fact, this is by far the broadest part of 

 the brain ; behind these lobes the brain graduall}^ tapers. 

 The brain may be roughly compared in shape to two slightly 

 flattened pears lying side by side with their narrower faces 

 adjacent and fused along the middle third of their length. 

 Tlie broad forwardly directed ends of the pears represent 

 the anterior cerebral lobes, while the tapering ends represent 

 the posterior lobes, which are continuous with two nerve- 

 tracts lying below the epithelium of the nuchal organ. The 

 anterior brain-lobes are separated in front by a cwlomic space. 

 Each gives off jinteriorly and dorsally a series of nerves 

 to the epithelium of the prostomium. The anterior part 

 of these lobes consists almost entirely of small cells situated 

 in clusters and sei)arated from one another by iibrous tracts 

 and by neuroglial tissue. Further back the delicate neuro- 

 pile which forms the core of these anterior lobes is well seen, 



' Sec also Child (1900), p. 592, for further observations on the ovu of A. 



cristata. 



