MUSEUM OF COMPARATIVE ZOOLOGY. 9 



animal selected — as usual, Glossiphonia. As in former years, 

 a certain number of lectures were given on the anatomy and his- 

 tology of this leech. 



The lectures in Zoology 5 were given by Professor Mark, as 

 usual, the ground covered being the general development of Ver- 

 tebrates, not including organogeny, but embracing the discussion 

 of many theoretical problems. The laboratory work in both Zool- 

 ogy 4 and 5 was under the supervision of Dr. Rand, who also super- 

 vised the laboratory exercises of Radcliffe students in Zoology 4. 



Both of Professor Jackson's courses on Fossil Invertebrates — 

 Zoology 9 and Zoology 9a — were given. It seems probable that 

 the plan of dividing Zoology 9 into two half-courses has been 

 justified by this year's experience. 



The general subjects dealt with by Dr. Castle in the lectures of 

 Zoology 11 were Variation and Heredity. The effects of close- 

 breeding and of cross-breeding in relation to variation, and the 

 subject of hybridization were considered in some detail, and, 

 among others, the following topics were discussed : the relation 

 of local races to species, especially when interbred; the part 

 played by sports in race-formation ; the nature and causes of 

 prepotency, telegony, xenia, grafts, and graft-hybrids. A number 

 of interesting topics were assigned to members of the class for 

 laboratory work, from several of which important results have 

 been obtained. 



Dr. Castle has himself continued his breeding experiments with 

 mice and with guinea pigs. Incidental to the main inquiry, which 

 has not yet reached a final solution, certain interesting problems 

 have arisen. A four-toed race of guinea pigs is being rapidly estab- 

 lished, certain individuals having yielded more than fifty per cent 

 of young that possess this peculiarity. As the race becomes es- 

 tablished, it is proposed to study statistically the heredity of the 

 four-toed character in cross-breeding with normal individuals. 

 An experiment of close-breeding with guinea pigs has been carried 

 successfully through several generations, and its results are being 

 carefully studied. 



Zoology 13 was conducted by Professor Parker as in 1900-01, 

 except for a few minor changes. In Zoology 15 there were, be- 

 sides the regularly enrolled students, three others who attended 

 all the lectures. Four of the topics assigned to individual students 

 for investigation have yielded results that are to be presented for 

 publication. 



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