262 E, RAY LANKESTER, 
Huxley has drawn attention to the very strongly marked 
plaiting or longitudinal grooving of the ventral integument. 
This is imperfectly figured by Stieda, but in specimens 
preserved in absolute alcohol it is very strongly marked. In 
cross-section of specimens preserved in picric acid (afterwards 
in alcohol) the longitudinal grooving is seen asa series of 
closely adpressed papillee (the cross-sections of longitudinal 
folds). ‘They vary in number from six to eight on each side 
of the median raphe, and are not always the same in number 
on the two sides. The epithelium which covers them does 
not differ from that of the rest of the surface of the body. 
Professor Huxley has observed these plaits in the living 
animal, and my friend Mr. Balfour, who has recently (at my 
request) been so obliging as to examine living specimens 
of Amphioxus at Naples as to their occurrence, reports 
that in the winter and spring (when, it must be remem- 
bered, the genital products are not fully developed) these 
‘ruge’ are always present, and can be seen without subject- 
ing the animal to any restraint. Mr. Balfour further states 
that the plaits differ sometimes in number on the two sides 
of the middle line, and also become more or less distinct 
according to the distension of the atrial cavity. 
I was led to ask for this information concerning the living 
Amphioxus since I have some specimens of the animal taken 
in May, when fully distended with ova (preserved first for 
a week in Miiller’s fluid, then in weak and subsequently in 
absolute alcohol), which specimens show in transverse sec- 
tions no trace of the plaited epithelium of the ventral sur- 
face. The atrial chamber is largely distended by the massive 
generative products and the ventral musculature and in- 
tegument is stretched out tight and smooth. What is still 
more remarkable in these specimens is the absence of the 
metapleura which were figured by Johannes Muller in 1842, 
and which in specimens preserved in absolute alcohol present 
the curious inflection towards the middle line, so as to 
form an incomplete subventral canal, as described by 
Professor Huxley and subsequently by Professor Wilhelm 
Miller in almost the same words, and as shown by many 
sections cut by Mr. Fanning and myself. It appears that 
in consequence of the distension of the atrial chamber 
by the swelling genitalia, not only are the plaits of the 
ventral integument smoothed away, but that the base of the 
triangle which the latero-ventral (metapleural) lymph space 
presents in transverse section, is so much stretched and in- 
creased in length that the angle opposite to the base becomes 
more and more obtuse and finally disappears, the two sides 
