2l8 HAROLD HEATH. 



the extreme posterior end of the animal through two small ves- 

 sels close to the mid-line behind and in certain cases even these 

 openings appear to be absent. 



The relations of the aorta to the heart and head cavity and the 

 origin of the genital arteries Middendorff correctly determined but 

 the account of the last-named vessels is somewhat obscure. A 

 careful examination shows that they course between the folds of 

 the inner wall of the gland very much as in Acanthopleura cchi- 

 nata ( Plate) and after branching repeatedly (and often not dichot- 

 omously) become lost among the developing sex products. 



Concerning the course of the blood from the gonad I have 

 nothing to add to Plate's account of Acanthopleura ccJnnata except 

 that in CryptocJiiton a relatively large quantity leaves from the 

 neighborhood of the gonoducts and enters the extensive sheets 

 of kidney tissue adjoining the front end of the pericardium. From 

 here very little blood appears to go into the visceral cavity but 

 penetrating the spongy tissue of what may be termed the lateral 

 space (Seitenluckenraum, Midd.; Lateralkammer, Plate) is poured 

 into the lateral sinus (Seitenarterie, Midd.). 



The dorsal arteries, lateral vessels between the II-V valves, 

 supply some of the shell muscles in the fashion accurately 

 described by Plate. Owing probably to the greater size of the 

 mantle in Cryptocldton the intersegmental arteries are more 

 numerous and of larger size than in other species of chitons. 

 They arise sometimes singly (dividing almost at once) though 

 usually in pairs from the dorsal side of the aorta between each 

 valve and as well defined vessels may be traced for considerable 

 distances. Usually these vessels do not extend far into a neigh- 

 boring "segment" but in all of the specimens carefully exam- 

 ined on this point the vessels between segment V-VI are in- 

 variably of large size and extending latterly and posteriorly 

 supply the greater part of the hinder portions of the mantle. 

 The blood returning from the pallium pours into the lateral sinus. 



Middendorff (p. 70) states that these small vessels (called by 

 him Mantelarterien) appear to end blindly in the leathery sub- 

 stance of the mantle and on the other hand to open into the 

 lateral sinus and the branchial artery. Plate also makes the 

 statement that in Acantlwpleura ccJdnata most if not all of the 



