11 



comparatively small, and they are seemingly shed almost continuously 

 during the winter and spring since they are rarely lacking from the gono- 

 ducts during these seasons. 



As noted in a previous paper (Heath 1905)3 these chitons inhabit 

 small elevated tide pools in which the water is rarely changed save by 

 the dash of the surf. And furthermore the young are brooded by the 

 parent as in the case of Chiton polii, Ischnochiton iiiiitator and two or 

 three other species. In the case of the present species a small number 

 of individuals are usually grouped closely together during the breeding 

 season, and under such circumstances a large number of spermatozoa 

 is not essential as with the majority of species. 



In this species the gonad arises at a very early period though I am 

 as yet somewhat in doubt as to its exakt mode of origin. In specimens 

 not yet 2 mm long it exists in the form of two small sacs in contact 

 with and partly overlapped by the forward end of the pericardium, and 

 the dorsal aorts passes between them as in the solenogastres. At this 

 time there is no evidence of an connection between the pericardial and 

 gonad cavities, and if the gonad arises, as I now believe, as two pro- 

 liferations of cells of the anterior pericardial wall and a cavity subse- 

 quently appears in each then there is at no time any such communication. 

 In this early stage clearly defined though very slender gonoducts lead 

 to the exterior. They extend from the posterior lateral angle of each 

 gonad sac and are in direct communication with it. In one specimen, 

 slightly over 1 mm long, these tubes end blindly in the neighbourhood of 

 the lateral nerve, and accordingly I am strongly of the opinion that 

 each gonoduct is almost wholly an outgrowth of the wall of the gonad 

 and not in large measure an ectodermal product, though an examination 

 of a larger number of specimens must be made before a definite sta- 

 tement may be made. The paired character of the gonad persists into 

 the late stages of development , but save for a slight indentation at its 

 anterior end (and this is frequently lacking) and the arrangement of the 

 branches of the aorta, as Plate (1. c. Teil A, p. 113) has noted, it dis- 

 appears in the adult. 



In not less than twelve species of chitons found on the California 

 coast the gonad and its ducts arise very early, invariably before the 

 animal is 3 mm in length. In Katharina tunicata^ for example, which 

 often reaches a length of 80 mm in an adult condition, this is the case, 

 the two gonad sacs and their ducts holding essentially the same relations 

 as those described for Tr. raymondi. As development progresses the 

 gonoducts usually become somewhat convoluted and at the same time 



3 Heath, The Breeding habits of Chitons of the California Coast. Zool. Anz. 

 Bd. XXIX. No. 12. pp. 390-393. 



